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 $160.83   3.397%   $166.2934   $166.29   $166.30   $166.30  
  Purchase #2 $62.92   3.576%   $65.17   $65.17   $65.15   $65.20  
  Purchase #3 $101.62   9.672%   $111.4487   $111.45   $111.45   $111.40  
  Purchase #4 $84.79   3.501%   $87.7585   $87.76   $87.75   $87.80  
  Purchase #5 $41.28   13.746%   $46.9543   $46.95   $46.95   $47.00  
  Purchase #6 $89.28   9.162%   $97.4598   $97.46   $97.45   $97.50  
  Purchase #7 $212.70   3.163%   $219.4277   $219.43   $219.45   $219.40  
  7 purchase totals = $753.42       $794.5124   $794.51   $794.50   $794.60