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 $75.47   10.293%   $83.2381   $83.24   $83.25   $83.20  
  Purchase #2 $118.83   11.421%   $132.4016   $132.40   $132.40   $132.40  
  Purchase #3 $75.69   5.332%   $79.7258   $79.73   $79.75   $79.70  
  Purchase #4 $248.47   11.729%   $277.613   $277.61   $277.60   $277.60  
  Purchase #5 $195.44   6.122%   $207.4048   $207.40   $207.40   $207.40  
  Purchase #6 $133.77   3.127%   $137.953   $137.95   $137.95   $138.00  
  Purchase #7 $222.40   8.621%   $241.5731   $241.57   $241.55   $241.60  
  7 purchase totals = $1,070.07       $1,159.9094   $1,159.90   $1,159.90   $1,159.90