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 $125.61   9.821%   $137.9462   $137.95   $137.95   $137.90  
  Purchase #2 $11.88   13.744%   $13.5128   $13.51   $13.50   $13.50  
  Purchase #3 $51.57   8.663%   $56.0375   $56.04   $56.05   $56.00  
  Purchase #4 $23.99   3.204%   $24.7586   $24.76   $24.75   $24.80  
  Purchase #5 $235.96   10.588%   $260.9434   $260.94   $260.95   $260.90  
  Purchase #6 $212.41   11.727%   $237.3193   $237.32   $237.30   $237.30  
  Purchase #7 $172.37   5.593%   $182.0107   $182.01   $182.00   $182.00  
  7 purchase totals = $833.79       $912.5285   $912.53   $912.50   $912.40