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 $93.46   11.667%   $104.364   $104.36   $104.35   $104.40  
  Purchase #2 $39.59   10.835%   $43.8796   $43.88   $43.90   $43.90  
  Purchase #3 $61.71   12.340%   $69.325   $69.33   $69.35   $69.30  
  Purchase #4 $45.26   13.271%   $51.2665   $51.27   $51.25   $51.30  
  Purchase #5 $240.65   6.526%   $256.3548   $256.35   $256.35   $256.40  
  Purchase #6 $44.81   8.228%   $48.497   $48.50   $48.50   $48.50  
  Purchase #7 $201.57   7.301%   $216.2866   $216.29   $216.30   $216.30  
  7 purchase totals = $727.05       $789.9735   $789.98   $790.00   $790.10