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 $43.27   7.252%   $46.4079   $46.41   $46.40   $46.40  
  Purchase #2 $222.73   9.609%   $244.1321   $244.13   $244.15   $244.10  
  Purchase #3 $182.36   5.414%   $192.233   $192.23   $192.25   $192.20  
  Purchase #4 $44.95   3.605%   $46.5704   $46.57   $46.55   $46.60  
  Purchase #5 $203.60   5.779%   $215.366   $215.37   $215.35   $215.40  
  Purchase #6 $59.54   5.184%   $62.6266   $62.63   $62.65   $62.60  
  Purchase #7 $100.30   6.652%   $106.972   $106.97   $106.95   $107.00  
  7 purchase totals = $856.75       $914.3080   $914.31   $914.30   $914.30