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 $86.36   11.474%   $96.2689   $96.27   $96.25   $96.30  
  Purchase #2 $197.76   13.653%   $224.7602   $224.76   $224.75   $224.80  
  Purchase #3 $197.95   9.652%   $217.0561   $217.06   $217.05   $217.10  
  Purchase #4 $90.48   12.810%   $102.0705   $102.07   $102.05   $102.10  
  Purchase #5 $212.56   10.251%   $234.3495   $234.35   $234.35   $234.30  
  Purchase #6 $175.69   3.819%   $182.3996   $182.40   $182.40   $182.40  
  Purchase #7 $206.47   4.684%   $216.1411   $216.14   $216.15   $216.10  
  7 purchase totals = $1,167.27       $1,273.0459   $1,273.05   $1,273.00   $1,273.10