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 $63.36   3.757%   $65.7404   $65.74   $65.75   $65.70  
  Purchase #2 $111.92   12.255%   $125.6358   $125.64   $125.65   $125.60  
  Purchase #3 $183.74   6.375%   $195.4534   $195.45   $195.45   $195.50  
  Purchase #4 $206.30   8.873%   $224.605   $224.61   $224.60   $224.60  
  Purchase #5 $7.38   7.179%   $7.9098   $7.91   $7.90   $7.90  
  Purchase #6 $69.70   10.475%   $77.0011   $77.00   $77.00   $77.00  
  Purchase #7 $133.47   11.264%   $148.5041   $148.50   $148.50   $148.50  
  7 purchase totals = $775.87       $844.8496   $844.85   $844.85   $844.80