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 $180.96   11.551%   $201.8627   $201.86   $201.85   $201.90  
  Purchase #2 $12.80   12.196%   $14.3611   $14.36   $14.35   $14.40  
  Purchase #3 $114.92   10.125%   $126.5557   $126.56   $126.55   $126.60  
  Purchase #4 $124.95   9.874%   $137.2876   $137.29   $137.30   $137.30  
  Purchase #5 $161.54   4.157%   $168.2552   $168.26   $168.25   $168.30  
  Purchase #6 $75.87   8.408%   $82.2491   $82.25   $82.25   $82.20  
  Purchase #7 $216.26   8.342%   $234.3004   $234.30   $234.30   $234.30  
  7 purchase totals = $887.30       $964.8718   $964.88   $964.85   $965.00