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 $106.84   8.764%   $116.2035   $116.20   $116.20   $116.20  
  Purchase #2 $37.84   12.790%   $42.6797   $42.68   $42.70   $42.70  
  Purchase #3 $228.35   9.228%   $249.4221   $249.42   $249.40   $249.40  
  Purchase #4 $93.76   4.492%   $97.9717   $97.97   $97.95   $98.00  
  Purchase #5 $95.34   13.228%   $107.9516   $107.95   $107.95   $108.00  
  Purchase #6 $9.84   13.690%   $11.1871   $11.19   $11.20   $11.20  
  Purchase #7 $132.46   5.346%   $139.5413   $139.54   $139.55   $139.50  
  7 purchase totals = $704.43       $764.9570   $764.95   $764.95   $765.00