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 $215.52   6.380%   $229.2702   $229.27   $229.25   $229.30  
  Purchase #2 $56.69   9.699%   $62.1884   $62.19   $62.20   $62.20  
  Purchase #3 $209.29   5.661%   $221.1379   $221.14   $221.15   $221.10  
  Purchase #4 $124.50   7.620%   $133.9869   $133.99   $134.00   $134.00  
  Purchase #5 $92.47   10.747%   $102.4078   $102.41   $102.40   $102.40  
  Purchase #6 $124.55   9.767%   $136.7148   $136.71   $136.70   $136.70  
  Purchase #7 $100.66   10.249%   $110.9766   $110.98   $111.00   $111.00  
  7 purchase totals = $923.68       $996.6826   $996.69   $996.70   $996.70