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 $241.76   6.255%   $256.8821   $256.88   $256.90   $256.90  
  Purchase #2 $65.72   9.293%   $71.8274   $71.83   $71.85   $71.80  
  Purchase #3 $9.34   6.686%   $9.9645   $9.96   $9.95   $10.00  
  Purchase #4 $128.30   4.369%   $133.9054   $133.91   $133.90   $133.90  
  Purchase #5 $88.62   9.742%   $97.2534   $97.25   $97.25   $97.30  
  Purchase #6 $55.64   11.812%   $62.2122   $62.21   $62.20   $62.20  
  Purchase #7 $83.36   10.290%   $91.9377   $91.94   $91.95   $91.90  
  7 purchase totals = $672.74       $723.9827   $723.98   $724.00   $724.00