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 $58.73   7.307%   $63.0214   $63.02   $63.00   $63.00  
  Purchase #2 $169.40   4.584%   $177.1653   $177.17   $177.15   $177.20  
  Purchase #3 $205.32   3.579%   $212.6684   $212.67   $212.65   $212.70  
  Purchase #4 $116.77   3.131%   $120.4261   $120.43   $120.45   $120.40  
  Purchase #5 $18.39   3.266%   $18.9906   $18.99   $19.00   $19.00  
  Purchase #6 $125.93   5.633%   $133.0236   $133.02   $133.00   $133.00  
  Purchase #7 $39.53   5.684%   $41.7769   $41.78   $41.80   $41.80  
  7 purchase totals = $734.07       $767.0723   $767.08   $767.05   $767.10