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 $58.30   8.795%   $63.4275   $63.43   $63.45   $63.40  
  Purchase #2 $209.73   11.108%   $233.0268   $233.03   $233.05   $233.00  
  Purchase #3 $34.71   5.520%   $36.626   $36.63   $36.65   $36.60  
  Purchase #4 $83.71   13.638%   $95.1264   $95.13   $95.15   $95.10  
  Purchase #5 $166.50   4.108%   $173.3398   $173.34   $173.35   $173.30  
  Purchase #6 $201.47   5.273%   $212.0935   $212.09   $212.10   $212.10  
  Purchase #7 $5.85   4.175%   $6.0942   $6.09   $6.10   $6.10  
  7 purchase totals = $760.27       $819.7342   $819.74   $819.85   $819.60