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 $54.46   6.365%   $57.9264   $57.93   $57.95   $57.90  
  Purchase #2 $119.81   5.293%   $126.1515   $126.15   $126.15   $126.20  
  Purchase #3 $154.93   3.580%   $160.4765   $160.48   $160.50   $160.50  
  Purchase #4 $240.47   8.445%   $260.7777   $260.78   $260.80   $260.80  
  Purchase #5 $40.48   11.464%   $45.1206   $45.12   $45.10   $45.10  
  Purchase #6 $113.75   11.321%   $126.6276   $126.63   $126.65   $126.60  
  Purchase #7 $97.57   6.747%   $104.153   $104.15   $104.15   $104.20  
  7 purchase totals = $821.47       $881.2333   $881.24   $881.30   $881.30