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 $239.26   11.692%   $267.2343   $267.23   $267.25   $267.20  
  Purchase #2 $18.39   11.148%   $20.4401   $20.44   $20.45   $20.40  
  Purchase #3 $204.74   13.443%   $232.2632   $232.26   $232.25   $232.30  
  Purchase #4 $52.34   9.767%   $57.452   $57.45   $57.45   $57.50  
  Purchase #5 $15.72   13.694%   $17.8727   $17.87   $17.85   $17.90  
  Purchase #6 $139.84   8.342%   $151.5055   $151.51   $151.50   $151.50  
  Purchase #7 $113.43   11.739%   $126.7455   $126.75   $126.75   $126.70  
  7 purchase totals = $783.72       $873.5133   $873.51   $873.50   $873.50