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 $124.87   7.301%   $133.9868   $133.99   $134.00   $134.00  
  Purchase #2 $125.75   11.770%   $140.5508   $140.55   $140.55   $140.60  
  Purchase #3 $98.47   3.443%   $101.8603   $101.86   $101.85   $101.90  
  Purchase #4 $78.85   3.681%   $81.7525   $81.75   $81.75   $81.80  
  Purchase #5 $166.64   11.246%   $185.3803   $185.38   $185.40   $185.40  
  Purchase #6 $123.72   12.238%   $138.8609   $138.86   $138.85   $138.90  
  Purchase #7 $64.74   12.752%   $72.9956   $73.00   $73.00   $73.00  
  7 purchase totals = $783.04       $855.3872   $855.39   $855.40   $855.60