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 $90.47   12.462%   $101.7444   $101.74   $101.75   $101.70  
  Purchase #2 $209.87   12.132%   $235.3314   $235.33   $235.35   $235.30  
  Purchase #3 $139.47   10.137%   $153.6081   $153.61   $153.60   $153.60  
  Purchase #4 $21.66   9.775%   $23.7773   $23.78   $23.80   $23.80  
  Purchase #5 $157.69   13.725%   $179.333   $179.33   $179.35   $179.30  
  Purchase #6 $52.41   5.427%   $55.2543   $55.25   $55.25   $55.30  
  Purchase #7 $130.27   13.754%   $148.1873   $148.19   $148.20   $148.20  
  7 purchase totals = $801.84       $897.2358   $897.23   $897.30   $897.20