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 $247.60   8.504%   $268.6559   $268.66   $268.65   $268.70  
  Purchase #2 $187.25   13.440%   $212.4164   $212.42   $212.40   $212.40  
  Purchase #3 $119.86   5.107%   $125.9813   $125.98   $126.00   $126.00  
  Purchase #4 $66.67   5.815%   $70.5469   $70.55   $70.55   $70.50  
  Purchase #5 $67.72   8.209%   $73.2791   $73.28   $73.30   $73.30  
  Purchase #6 $15.65   3.546%   $16.2049   $16.20   $16.20   $16.20  
  Purchase #7 $92.41   9.202%   $100.9136   $100.91   $100.90   $100.90  
  7 purchase totals = $797.16       $867.9981   $868.00   $868.00   $868.00