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 $62.93   3.785%   $65.3119   $65.31   $65.30   $65.30  
  Purchase #2 $232.54   5.536%   $245.4134   $245.41   $245.40   $245.40  
  Purchase #3 $46.26   10.254%   $51.0035   $51.00   $51.00   $51.00  
  Purchase #4 $137.41   10.594%   $151.9672   $151.97   $151.95   $152.00  
  Purchase #5 $31.92   12.733%   $35.9844   $35.98   $36.00   $36.00  
  Purchase #6 $243.98   12.407%   $274.2506   $274.25   $274.25   $274.30  
  Purchase #7 $52.69   3.227%   $54.3903   $54.39   $54.40   $54.40  
  7 purchase totals = $807.73       $878.3213   $878.31   $878.30   $878.40