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 $87.53   13.610%   $99.4428   $99.44   $99.45   $99.40  
  Purchase #2 $235.38   4.448%   $245.8497   $245.85   $245.85   $245.80  
  Purchase #3 $133.68   6.748%   $142.7007   $142.70   $142.70   $142.70  
  Purchase #4 $131.31   4.544%   $137.2767   $137.28   $137.30   $137.30  
  Purchase #5 $62.34   10.549%   $68.9162   $68.92   $68.90   $68.90  
  Purchase #6 $204.33   12.459%   $229.7875   $229.79   $229.80   $229.80  
  Purchase #7 $8.34   3.603%   $8.6405   $8.64   $8.65   $8.60  
  7 purchase totals = $862.91       $932.6141   $932.62   $932.65   $932.50