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 $108.32   7.626%   $116.5805   $116.58   $116.60   $116.60  
  Purchase #2 $56.74   7.733%   $61.1277   $61.13   $61.15   $61.10  
  Purchase #3 $211.90   8.441%   $229.7865   $229.79   $229.80   $229.80  
  Purchase #4 $150.60   7.525%   $161.9327   $161.93   $161.95   $161.90  
  Purchase #5 $8.83   13.409%   $10.014   $10.01   $10.00   $10.00  
  Purchase #6 $149.99   3.526%   $155.2786   $155.28   $155.30   $155.30  
  Purchase #7 $93.56   8.593%   $101.5996   $101.60   $101.60   $101.60  
  7 purchase totals = $779.94       $836.3196   $836.32   $836.40   $836.30