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 $23.97   4.493%   $25.047   $25.05   $25.05   $25.00  
  Purchase #2 $232.59   6.115%   $246.8129   $246.81   $246.80   $246.80  
  Purchase #3 $48.26   3.790%   $50.0891   $50.09   $50.10   $50.10  
  Purchase #4 $65.87   6.753%   $70.3182   $70.32   $70.30   $70.30  
  Purchase #5 $146.25   4.274%   $152.5007   $152.50   $152.50   $152.50  
  Purchase #6 $174.73   4.686%   $182.9178   $182.92   $182.90   $182.90  
  Purchase #7 $102.66   6.196%   $109.0208   $109.02   $109.00   $109.00  
  7 purchase totals = $794.33       $836.7065   $836.71   $836.65   $836.60