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 $184.73   12.204%   $207.2744   $207.27   $207.25   $207.30  
  Purchase #2 $233.46   11.414%   $260.1071   $260.11   $260.10   $260.10  
  Purchase #3 $248.44   12.180%   $278.7   $278.70   $278.70   $278.70  
  Purchase #4 $219.54   7.687%   $236.416   $236.42   $236.40   $236.40  
  Purchase #5 $88.44   5.715%   $93.4943   $93.49   $93.50   $93.50  
  Purchase #6 $195.49   11.719%   $218.3995   $218.40   $218.40   $218.40  
  Purchase #7 $131.97   12.675%   $148.6972   $148.70   $148.70   $148.70  
  7 purchase totals = $1,302.07       $1,443.0885   $1,443.09   $1,443.05   $1,443.10