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 $42.86   12.151%   $48.0679   $48.07   $48.05   $48.10  
  Purchase #2 $99.69   11.308%   $110.9629   $110.96   $110.95   $111.00  
  Purchase #3 $209.62   9.554%   $229.6471   $229.65   $229.65   $229.60  
  Purchase #4 $95.99   12.237%   $107.7363   $107.74   $107.75   $107.70  
  Purchase #5 $113.79   10.705%   $125.9712   $125.97   $125.95   $126.00  
  Purchase #6 $52.81   4.806%   $55.348   $55.35   $55.35   $55.30  
  Purchase #7 $80.87   6.681%   $86.2729   $86.27   $86.25   $86.30  
  7 purchase totals = $695.63       $764.0063   $764.01   $763.95   $764.00