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 $68.93   11.522%   $76.8721   $76.87   $76.85   $76.90  
  Purchase #2 $66.69   6.756%   $71.1956   $71.20   $71.20   $71.20  
  Purchase #3 $124.91   11.153%   $138.8412   $138.84   $138.85   $138.80  
  Purchase #4 $67.53   10.853%   $74.859   $74.86   $74.85   $74.90  
  Purchase #5 $202.48   4.839%   $212.278   $212.28   $212.30   $212.30  
  Purchase #6 $36.34   7.726%   $39.1476   $39.15   $39.15   $39.10  
  Purchase #7 $93.56   10.872%   $103.7318   $103.73   $103.75   $103.70  
  7 purchase totals = $660.44       $716.9253   $716.93   $716.95   $716.90