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 $67.75   11.430%   $75.4938   $75.49   $75.50   $75.50  
  Purchase #2 $58.89   13.190%   $66.6576   $66.66   $66.65   $66.70  
  Purchase #3 $195.90   5.594%   $206.8586   $206.86   $206.85   $206.90  
  Purchase #4 $45.51   6.441%   $48.4413   $48.44   $48.45   $48.40  
  Purchase #5 $222.80   11.264%   $247.8962   $247.90   $247.90   $247.90  
  Purchase #6 $29.53   12.275%   $33.1548   $33.15   $33.15   $33.20  
  Purchase #7 $8.49   11.821%   $9.4936   $9.49   $9.50   $9.50  
  7 purchase totals = $628.87       $687.9959   $687.99   $688.00   $688.10