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 $196.69   3.317%   $203.2142   $203.21   $203.20   $203.20  
  Purchase #2 $231.25   7.231%   $247.9717   $247.97   $247.95   $248.00  
  Purchase #3 $154.51   9.623%   $169.3785   $169.38   $169.40   $169.40  
  Purchase #4 $195.83   10.833%   $217.0443   $217.04   $217.05   $217.00  
  Purchase #5 $92.84   3.223%   $95.8322   $95.83   $95.85   $95.80  
  Purchase #6 $8.73   11.396%   $9.7249   $9.72   $9.70   $9.70  
  Purchase #7 $76.58   10.151%   $84.3536   $84.35   $84.35   $84.40  
  7 purchase totals = $956.43       $1,027.5194   $1,027.50   $1,027.50   $1,027.50