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 $54.67   13.352%   $61.9695   $61.97   $61.95   $62.00  
  Purchase #2 $139.55   12.194%   $156.5667   $156.57   $156.55   $156.60  
  Purchase #3 $151.95   6.763%   $162.2264   $162.23   $162.25   $162.20  
  Purchase #4 $19.26   12.162%   $21.6024   $21.60   $21.60   $21.60  
  Purchase #5 $71.37   4.554%   $74.6202   $74.62   $74.60   $74.60  
  Purchase #6 $214.34   13.549%   $243.3809   $243.38   $243.40   $243.40  
  Purchase #7 $57.56   4.776%   $60.3091   $60.31   $60.30   $60.30  
  7 purchase totals = $708.70       $780.6752   $780.68   $780.65   $780.70