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 $246.85   7.636%   $265.6995   $265.70   $265.70   $265.70  
  Purchase #2 $227.94   11.186%   $253.4374   $253.44   $253.45   $253.40  
  Purchase #3 $199.39   11.473%   $222.266   $222.27   $222.25   $222.30  
  Purchase #4 $216.79   3.215%   $223.7598   $223.76   $223.75   $223.80  
  Purchase #5 $86.79   11.549%   $96.8134   $96.81   $96.80   $96.80  
  Purchase #6 $56.97   5.538%   $60.125   $60.13   $60.15   $60.10  
  Purchase #7 $142.90   4.355%   $149.1233   $149.12   $149.10   $149.10  
  7 purchase totals = $1,177.63       $1,271.2244   $1,271.23   $1,271.20   $1,271.20