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 $233.76   5.586%   $246.8178   $246.82   $246.80   $246.80  
  Purchase #2 $119.27   5.104%   $125.3575   $125.36   $125.35   $125.40  
  Purchase #3 $156.34   9.373%   $170.9937   $170.99   $171.00   $171.00  
  Purchase #4 $229.66   5.730%   $242.8195   $242.82   $242.80   $242.80  
  Purchase #5 $206.42   3.638%   $213.9296   $213.93   $213.95   $213.90  
  Purchase #6 $146.93   7.485%   $157.9277   $157.93   $157.95   $157.90  
  Purchase #7 $195.96   10.644%   $216.818   $216.82   $216.80   $216.80  
  7 purchase totals = $1,288.34       $1,374.6638   $1,374.67   $1,374.65   $1,374.60