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 $208.88   11.861%   $233.6553   $233.66   $233.65   $233.70  
  Purchase #2 $20.70   11.210%   $23.0205   $23.02   $23.00   $23.00  
  Purchase #3 $112.45   11.856%   $125.7821   $125.78   $125.80   $125.80  
  Purchase #4 $50.55   13.602%   $57.4258   $57.43   $57.45   $57.40  
  Purchase #5 $146.83   8.291%   $159.0037   $159.00   $159.00   $159.00  
  Purchase #6 $226.77   12.476%   $255.0618   $255.06   $255.05   $255.10  
  Purchase #7 $193.65   11.499%   $215.9178   $215.92   $215.90   $215.90  
  7 purchase totals = $959.83       $1,069.8670   $1,069.87   $1,069.85   $1,069.90