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 $22.92   8.805%   $24.9381   $24.94   $24.95   $24.90  
  Purchase #2 $191.88   13.589%   $217.9546   $217.95   $217.95   $218.00  
  Purchase #3 $215.61   6.244%   $229.0727   $229.07   $229.05   $229.10  
  Purchase #4 $180.78   9.164%   $197.3467   $197.35   $197.35   $197.30  
  Purchase #5 $190.25   8.756%   $206.9083   $206.91   $206.90   $206.90  
  Purchase #6 $7.98   11.370%   $8.8873   $8.89   $8.90   $8.90  
  Purchase #7 $174.52   11.506%   $194.6003   $194.60   $194.60   $194.60  
  7 purchase totals = $983.94       $1,079.7080   $1,079.71   $1,079.70   $1,079.70