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 $229.92   13.709%   $261.4397   $261.44   $261.45   $261.40  
  Purchase #2 $219.35   12.727%   $247.2667   $247.27   $247.25   $247.30  
  Purchase #3 $95.52   13.327%   $108.25   $108.25   $108.25   $108.30  
  Purchase #4 $8.67   5.509%   $9.1476   $9.15   $9.15   $9.10  
  Purchase #5 $167.64   9.132%   $182.9489   $182.95   $182.95   $182.90  
  Purchase #6 $5.30   8.797%   $5.7662   $5.77   $5.75   $5.80  
  Purchase #7 $180.25   12.155%   $202.1594   $202.16   $202.15   $202.20  
  7 purchase totals = $906.65       $1,016.9785   $1,016.99   $1,016.95   $1,017.00