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 $68.29   11.627%   $76.2301   $76.23   $76.25   $76.20  
  Purchase #2 $207.36   3.838%   $215.3185   $215.32   $215.30   $215.30  
  Purchase #3 $187.96   11.803%   $210.1449   $210.14   $210.15   $210.10  
  Purchase #4 $208.25   11.253%   $231.6844   $231.68   $231.70   $231.70  
  Purchase #5 $32.65   5.504%   $34.4471   $34.45   $34.45   $34.40  
  Purchase #6 $24.29   4.585%   $25.4037   $25.40   $25.40   $25.40  
  Purchase #7 $178.56   5.631%   $188.6147   $188.61   $188.60   $188.60  
  7 purchase totals = $907.36       $981.8434   $981.83   $981.85   $981.70