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 $208.92   4.492%   $218.3047   $218.30   $218.30   $218.30  
  Purchase #2 $249.46   4.840%   $261.5339   $261.53   $261.55   $261.50  
  Purchase #3 $64.38   6.309%   $68.4417   $68.44   $68.45   $68.40  
  Purchase #4 $154.73   8.385%   $167.7041   $167.70   $167.70   $167.70  
  Purchase #5 $205.57   3.350%   $212.4566   $212.46   $212.45   $212.50  
  Purchase #6 $236.68   10.758%   $262.142   $262.14   $262.15   $262.10  
  Purchase #7 $42.57   10.462%   $47.0237   $47.02   $47.00   $47.00  
  7 purchase totals = $1,162.31       $1,237.6067   $1,237.59   $1,237.60   $1,237.50