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 $125.96   9.276%   $137.644   $137.64   $137.65   $137.60  
  Purchase #2 $94.59   6.787%   $101.0098   $101.01   $101.00   $101.00  
  Purchase #3 $131.95   12.566%   $148.5308   $148.53   $148.55   $148.50  
  Purchase #4 $81.60   12.808%   $92.0513   $92.05   $92.05   $92.10  
  Purchase #5 $186.99   4.232%   $194.9034   $194.90   $194.90   $194.90  
  Purchase #6 $249.98   9.608%   $273.9981   $274.00   $274.00   $274.00  
  Purchase #7 $112.61   5.796%   $119.1369   $119.14   $119.15   $119.10  
  7 purchase totals = $983.68       $1,067.2743   $1,067.27   $1,067.30   $1,067.20