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 $23.95   9.756%   $26.2866   $26.29   $26.30   $26.30  
  Purchase #2 $75.72   12.283%   $85.0207   $85.02   $85.00   $85.00  
  Purchase #3 $13.97   7.535%   $15.0226   $15.02   $15.00   $15.00  
  Purchase #4 $238.98   3.143%   $246.4911   $246.49   $246.50   $246.50  
  Purchase #5 $17.56   3.305%   $18.1404   $18.14   $18.15   $18.10  
  Purchase #6 $20.49   3.520%   $21.2112   $21.21   $21.20   $21.20  
  Purchase #7 $183.75   12.240%   $206.241   $206.24   $206.25   $206.20  
  7 purchase totals = $574.42       $618.4136   $618.41   $618.40   $618.30