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 $95.91   3.381%   $99.1527   $99.15   $99.15   $99.20  
  Purchase #2 $196.74   8.113%   $212.7015   $212.70   $212.70   $212.70  
  Purchase #3 $15.38   12.387%   $17.2851   $17.29   $17.30   $17.30  
  Purchase #4 $107.58   11.300%   $119.7365   $119.74   $119.75   $119.70  
  Purchase #5 $29.29   5.622%   $30.9367   $30.94   $30.95   $30.90  
  Purchase #6 $197.66   3.306%   $204.1946   $204.19   $204.20   $204.20  
  Purchase #7 $240.67   7.130%   $257.8298   $257.83   $257.85   $257.80  
  7 purchase totals = $883.23       $941.8369   $941.84   $941.90   $941.80