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 $92.68   12.137%   $103.9286   $103.93   $103.95   $103.90  
  Purchase #2 $126.51   6.527%   $134.7673   $134.77   $134.75   $134.80  
  Purchase #3 $53.86   13.231%   $60.9862   $60.99   $61.00   $61.00  
  Purchase #4 $59.31   4.161%   $61.7779   $61.78   $61.80   $61.80  
  Purchase #5 $161.32   4.763%   $169.0037   $169.00   $169.00   $169.00  
  Purchase #6 $110.86   5.857%   $117.3531   $117.35   $117.35   $117.40  
  Purchase #7 $61.86   7.103%   $66.2539   $66.25   $66.25   $66.30  
  7 purchase totals = $666.40       $714.0707   $714.07   $714.10   $714.20