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 $94.41   10.194%   $104.0342   $104.03   $104.05   $104.00  
  Purchase #2 $38.42   7.310%   $41.2285   $41.23   $41.25   $41.20  
  Purchase #3 $73.49   6.160%   $78.017   $78.02   $78.00   $78.00  
  Purchase #4 $53.94   8.463%   $58.5049   $58.50   $58.50   $58.50  
  Purchase #5 $91.76   10.786%   $101.6572   $101.66   $101.65   $101.70  
  Purchase #6 $35.42   11.665%   $39.5517   $39.55   $39.55   $39.60  
  Purchase #7 $24.29   8.183%   $26.2777   $26.28   $26.30   $26.30  
  7 purchase totals = $411.73       $449.2712   $449.27   $449.30   $449.30