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 $55.97   11.741%   $62.5414   $62.54   $62.55   $62.50  
  Purchase #2 $152.55   7.447%   $163.9104   $163.91   $163.90   $163.90  
  Purchase #3 $86.94   11.827%   $97.2224   $97.22   $97.20   $97.20  
  Purchase #4 $199.78   6.574%   $212.9135   $212.91   $212.90   $212.90  
  Purchase #5 $55.62   8.726%   $60.4734   $60.47   $60.45   $60.50  
  Purchase #6 $31.56   4.250%   $32.9013   $32.90   $32.90   $32.90  
  Purchase #7 $49.36   5.330%   $51.9909   $51.99   $52.00   $52.00  
  7 purchase totals = $631.78       $681.9533   $681.94   $681.90   $681.90