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 $180.56   8.505%   $195.9166   $195.92   $195.90   $195.90  
  Purchase #2 $57.66   8.810%   $62.7398   $62.74   $62.75   $62.70  
  Purchase #3 $198.63   9.399%   $217.2992   $217.30   $217.30   $217.30  
  Purchase #4 $56.71   6.427%   $60.3548   $60.35   $60.35   $60.40  
  Purchase #5 $61.67   11.271%   $68.6208   $68.62   $68.60   $68.60  
  Purchase #6 $49.84   6.417%   $53.0382   $53.04   $53.05   $53.00  
  Purchase #7 $76.52   8.286%   $82.8604   $82.86   $82.85   $82.90  
  7 purchase totals = $681.59       $740.8298   $740.83   $740.80   $740.80