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 $210.41   5.481%   $221.9426   $221.94   $221.95   $221.90  
  Purchase #2 $234.78   6.195%   $249.3246   $249.32   $249.30   $249.30  
  Purchase #3 $237.42   11.428%   $264.5524   $264.55   $264.55   $264.60  
  Purchase #4 $87.74   4.327%   $91.5365   $91.54   $91.55   $91.50  
  Purchase #5 $154.84   6.531%   $164.9526   $164.95   $164.95   $165.00  
  Purchase #6 $215.88   3.853%   $224.1979   $224.20   $224.20   $224.20  
  Purchase #7 $74.41   6.628%   $79.3419   $79.34   $79.35   $79.30  
  7 purchase totals = $1,215.48       $1,295.8485   $1,295.84   $1,295.85   $1,295.80