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 $48.92   5.514%   $51.6174   $51.62   $51.60   $51.60  
  Purchase #2 $85.47   11.402%   $95.2153   $95.22   $95.20   $95.20  
  Purchase #3 $237.27   11.693%   $265.014   $265.01   $265.00   $265.00  
  Purchase #4 $197.59   10.174%   $217.6928   $217.69   $217.70   $217.70  
  Purchase #5 $126.36   13.159%   $142.9877   $142.99   $143.00   $143.00  
  Purchase #6 $158.39   6.491%   $168.6711   $168.67   $168.65   $168.70  
  Purchase #7 $40.96   13.496%   $46.488   $46.49   $46.50   $46.50  
  7 purchase totals = $894.96       $987.6863   $987.69   $987.65   $987.70