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 $66.49   13.224%   $75.2826   $75.28   $75.30   $75.30  
  Purchase #2 $38.71   11.141%   $43.0227   $43.02   $43.00   $43.00  
  Purchase #3 $77.38   13.538%   $87.8557   $87.86   $87.85   $87.90  
  Purchase #4 $195.41   11.206%   $217.3076   $217.31   $217.30   $217.30  
  Purchase #5 $233.92   9.210%   $255.464   $255.46   $255.45   $255.50  
  Purchase #6 $237.69   4.565%   $248.5405   $248.54   $248.55   $248.50  
  Purchase #7 $61.57   3.792%   $63.9047   $63.90   $63.90   $63.90  
  7 purchase totals = $911.17       $991.3778   $991.37   $991.35   $991.40