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 $73.95   12.779%   $83.4001   $83.40   $83.40   $83.40  
  Purchase #2 $188.26   11.118%   $209.1907   $209.19   $209.20   $209.20  
  Purchase #3 $227.72   9.657%   $249.7109   $249.71   $249.70   $249.70  
  Purchase #4 $111.74   9.447%   $122.2961   $122.30   $122.30   $122.30  
  Purchase #5 $171.90   5.157%   $180.7649   $180.76   $180.75   $180.80  
  Purchase #6 $54.67   12.505%   $61.5065   $61.51   $61.50   $61.50  
  Purchase #7 $136.89   12.498%   $153.9985   $154.00   $154.00   $154.00  
  7 purchase totals = $965.13       $1,060.8677   $1,060.87   $1,060.85   $1,060.90