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 $24.73   3.641%   $25.6304   $25.63   $25.65   $25.60  
  Purchase #2 $160.56   8.764%   $174.6315   $174.63   $174.65   $174.60  
  Purchase #3 $77.39   5.204%   $81.4174   $81.42   $81.40   $81.40  
  Purchase #4 $126.40   8.385%   $136.9986   $137.00   $137.00   $137.00  
  Purchase #5 $214.51   6.746%   $228.9808   $228.98   $229.00   $229.00  
  Purchase #6 $68.85   12.130%   $77.2015   $77.20   $77.20   $77.20  
  Purchase #7 $190.43   8.453%   $206.527   $206.53   $206.55   $206.50  
  7 purchase totals = $862.87       $931.3872   $931.39   $931.45   $931.30