Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $207.88   12.440%   $233.7403   $233.74   $233.75   $233.70  
  Purchase #2 $105.77   12.621%   $119.1192   $119.12   $119.10   $119.10  
  Purchase #3 $188.77   11.225%   $209.9594   $209.96   $209.95   $210.00  
  Purchase #4 $183.44   11.415%   $204.3797   $204.38   $204.40   $204.40  
  Purchase #5 $224.66   10.417%   $248.0628   $248.06   $248.05   $248.10  
  Purchase #6 $243.53   5.228%   $256.2617   $256.26   $256.25   $256.30  
  Purchase #7 $117.49   13.375%   $133.2043   $133.20   $133.20   $133.20  
  7 purchase totals = $1,271.54       $1,404.7274   $1,404.72   $1,404.70   $1,404.80