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 $15.39   3.627%   $15.9482   $15.95   $15.95   $15.90  
  Purchase #2 $237.75   7.643%   $255.9212   $255.92   $255.90   $255.90  
  Purchase #3 $40.87   12.791%   $46.0977   $46.10   $46.10   $46.10  
  Purchase #4 $40.27   4.208%   $41.9646   $41.96   $41.95   $42.00  
  Purchase #5 $240.66   7.638%   $259.0416   $259.04   $259.05   $259.00  
  Purchase #6 $99.77   7.644%   $107.3964   $107.40   $107.40   $107.40  
  Purchase #7 $133.90   7.652%   $144.146   $144.15   $144.15   $144.10  
  7 purchase totals = $808.61       $870.5157   $870.52   $870.50   $870.40