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 $17.60   5.369%   $18.5449   $18.54   $18.55   $18.50  
  Purchase #2 $185.73   6.476%   $197.7579   $197.76   $197.75   $197.80  
  Purchase #3 $53.62   4.272%   $55.9106   $55.91   $55.90   $55.90  
  Purchase #4 $140.71   13.770%   $160.0858   $160.09   $160.10   $160.10  
  Purchase #5 $21.88   8.503%   $23.7405   $23.74   $23.75   $23.70  
  Purchase #6 $51.44   13.868%   $58.5737   $58.57   $58.55   $58.60  
  Purchase #7 $8.82   9.717%   $9.677   $9.68   $9.70   $9.70  
  7 purchase totals = $479.80       $524.2904   $524.29   $524.30   $524.30