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 $176.31   11.650%   $196.8501   $196.85   $196.85   $196.90  
  Purchase #2 $155.37   9.597%   $170.2809   $170.28   $170.30   $170.30  
  Purchase #3 $93.56   11.574%   $104.3886   $104.39   $104.40   $104.40  
  Purchase #4 $12.73   12.119%   $14.2727   $14.27   $14.25   $14.30  
  Purchase #5 $140.64   5.234%   $148.0011   $148.00   $148.00   $148.00  
  Purchase #6 $87.45   3.811%   $90.7827   $90.78   $90.80   $90.80  
  Purchase #7 $195.99   9.504%   $214.6169   $214.62   $214.60   $214.60  
  7 purchase totals = $862.05       $939.1930   $939.19   $939.20   $939.30