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 $107.83   9.868%   $118.4707   $118.47   $118.45   $118.50  
  Purchase #2 $106.26   5.383%   $111.98   $111.98   $112.00   $112.00  
  Purchase #3 $59.86   5.825%   $63.3468   $63.35   $63.35   $63.30  
  Purchase #4 $242.46   4.872%   $254.2727   $254.27   $254.25   $254.30  
  Purchase #5 $73.66   8.518%   $79.9344   $79.93   $79.95   $79.90  
  Purchase #6 $72.59   4.726%   $76.0206   $76.02   $76.00   $76.00  
  Purchase #7 $38.98   5.523%   $41.1329   $41.13   $41.15   $41.10  
  7 purchase totals = $701.64       $745.1581   $745.15   $745.15   $745.10