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 $207.39   11.197%   $230.6115   $230.61   $230.60   $230.60  
  Purchase #2 $22.35   12.601%   $25.1663   $25.17   $25.15   $25.20  
  Purchase #3 $106.54   9.770%   $116.949   $116.95   $116.95   $116.90  
  Purchase #4 $54.29   5.386%   $57.2141   $57.21   $57.20   $57.20  
  Purchase #5 $12.34   8.609%   $13.4024   $13.40   $13.40   $13.40  
  Purchase #6 $53.48   8.517%   $58.0349   $58.03   $58.05   $58.00  
  Purchase #7 $9.35   13.212%   $10.5853   $10.59   $10.60   $10.60  
  7 purchase totals = $465.74       $511.9635   $511.96   $511.95   $511.90