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 $216.75   12.849%   $244.6002   $244.60   $244.60   $244.60  
  Purchase #2 $150.41   12.655%   $169.4444   $169.44   $169.45   $169.40  
  Purchase #3 $81.63   11.618%   $91.1138   $91.11   $91.10   $91.10  
  Purchase #4 $206.57   10.863%   $229.0097   $229.01   $229.00   $229.00  
  Purchase #5 $242.75   12.572%   $273.2685   $273.27   $273.25   $273.30  
  Purchase #6 $42.66   3.230%   $44.0379   $44.04   $44.05   $44.00  
  Purchase #7 $180.98   7.856%   $195.1978   $195.20   $195.20   $195.20  
  7 purchase totals = $1,121.75       $1,246.6723   $1,246.67   $1,246.65   $1,246.60