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 $93.49   12.183%   $104.8799   $104.88   $104.90   $104.90  
  Purchase #2 $118.70   11.521%   $132.3754   $132.38   $132.40   $132.40  
  Purchase #3 $62.62   4.144%   $65.215   $65.22   $65.20   $65.20  
  Purchase #4 $131.34   9.522%   $143.8462   $143.85   $143.85   $143.80  
  Purchase #5 $108.68   6.350%   $115.5812   $115.58   $115.60   $115.60  
  Purchase #6 $25.45   3.482%   $26.3362   $26.34   $26.35   $26.30  
  Purchase #7 $121.39   3.577%   $125.7321   $125.73   $125.75   $125.70  
  7 purchase totals = $661.67       $713.9660   $713.98   $714.05   $713.90