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 $108.99   9.751%   $119.6176   $119.62   $119.60   $119.60  
  Purchase #2 $233.54   6.291%   $248.232   $248.23   $248.25   $248.20  
  Purchase #3 $191.77   6.619%   $204.4633   $204.46   $204.45   $204.50  
  Purchase #4 $167.82   4.172%   $174.8215   $174.82   $174.80   $174.80  
  Purchase #5 $7.57   4.366%   $7.9005   $7.90   $7.90   $7.90  
  Purchase #6 $207.26   8.583%   $225.0491   $225.05   $225.05   $225.00  
  Purchase #7 $119.83   11.808%   $133.9795   $133.98   $134.00   $134.00  
  7 purchase totals = $1,036.78       $1,114.0635   $1,114.06   $1,114.05   $1,114.00