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 $236.39   10.134%   $260.3458   $260.35   $260.35   $260.30  
  Purchase #2 $217.43   9.400%   $237.8684   $237.87   $237.85   $237.90  
  Purchase #3 $199.85   6.706%   $213.2519   $213.25   $213.25   $213.30  
  Purchase #4 $205.49   4.219%   $214.1596   $214.16   $214.15   $214.20  
  Purchase #5 $66.76   3.349%   $68.9958   $69.00   $69.00   $69.00  
  Purchase #6 $180.58   4.795%   $189.2388   $189.24   $189.25   $189.20  
  Purchase #7 $70.77   3.184%   $73.0233   $73.02   $73.00   $73.00  
  7 purchase totals = $1,177.27       $1,256.8836   $1,256.89   $1,256.85   $1,256.90