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 $244.63   11.697%   $273.2444   $273.24   $273.25   $273.20  
  Purchase #2 $98.89   13.240%   $111.983   $111.98   $112.00   $112.00  
  Purchase #3 $30.62   10.701%   $33.8966   $33.90   $33.90   $33.90  
  Purchase #4 $20.36   7.686%   $21.9249   $21.92   $21.90   $21.90  
  Purchase #5 $139.59   9.578%   $152.9599   $152.96   $152.95   $153.00  
  Purchase #6 $149.61   9.361%   $163.615   $163.62   $163.60   $163.60  
  Purchase #7 $238.66   7.422%   $256.3733   $256.37   $256.35   $256.40  
  7 purchase totals = $922.36       $1,013.9971   $1,013.99   $1,013.95   $1,014.00