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 $104.92   6.476%   $111.7146   $111.71   $111.70   $111.70  
  Purchase #2 $159.46   11.187%   $177.2988   $177.30   $177.30   $177.30  
  Purchase #3 $154.79   5.148%   $162.7586   $162.76   $162.75   $162.80  
  Purchase #4 $125.98   5.557%   $132.9807   $132.98   $133.00   $133.00  
  Purchase #5 $208.97   9.605%   $229.0416   $229.04   $229.05   $229.00  
  Purchase #6 $179.48   11.642%   $200.3751   $200.38   $200.40   $200.40  
  Purchase #7 $87.33   12.770%   $98.482   $98.48   $98.50   $98.50  
  7 purchase totals = $1,020.93       $1,112.6514   $1,112.65   $1,112.70   $1,112.70