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 $241.49   7.675%   $260.0244   $260.02   $260.00   $260.00  
  Purchase #2 $195.71   6.406%   $208.2472   $208.25   $208.25   $208.20  
  Purchase #3 $25.78   3.532%   $26.6905   $26.69   $26.70   $26.70  
  Purchase #4 $6.84   10.622%   $7.5665   $7.57   $7.55   $7.60  
  Purchase #5 $12.27   4.145%   $12.7786   $12.78   $12.80   $12.80  
  Purchase #6 $209.31   4.683%   $219.112   $219.11   $219.10   $219.10  
  Purchase #7 $41.63   6.535%   $44.3505   $44.35   $44.35   $44.40  
  7 purchase totals = $733.03       $778.7697   $778.77   $778.75   $778.80