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 $60.76   9.659%   $66.6288   $66.63   $66.65   $66.60  
  Purchase #2 $111.79   13.197%   $126.5429   $126.54   $126.55   $126.50  
  Purchase #3 $30.35   12.695%   $34.2029   $34.20   $34.20   $34.20  
  Purchase #4 $112.75   7.651%   $121.3765   $121.38   $121.40   $121.40  
  Purchase #5 $169.38   4.782%   $177.4798   $177.48   $177.50   $177.50  
  Purchase #6 $248.61   4.574%   $259.9814   $259.98   $260.00   $260.00  
  Purchase #7 $72.56   6.211%   $77.0667   $77.07   $77.05   $77.10  
  7 purchase totals = $806.20       $863.2790   $863.28   $863.35   $863.30