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 $43.35   10.151%   $47.7505   $47.75   $47.75   $47.80  
  Purchase #2 $109.54   7.213%   $117.4411   $117.44   $117.45   $117.40  
  Purchase #3 $54.67   11.734%   $61.085   $61.09   $61.10   $61.10  
  Purchase #4 $195.92   8.645%   $212.8573   $212.86   $212.85   $212.90  
  Purchase #5 $234.65   6.268%   $249.3579   $249.36   $249.35   $249.40  
  Purchase #6 $187.34   12.526%   $210.8062   $210.81   $210.80   $210.80  
  Purchase #7 $61.50   8.397%   $66.6642   $66.66   $66.65   $66.70  
  7 purchase totals = $886.97       $965.9622   $965.97   $965.95   $966.10