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 $116.51   8.608%   $126.5392   $126.54   $126.55   $126.50  
  Purchase #2 $119.88   4.813%   $125.6498   $125.65   $125.65   $125.60  
  Purchase #3 $50.75   9.296%   $55.4677   $55.47   $55.45   $55.50  
  Purchase #4 $225.53   9.229%   $246.3442   $246.34   $246.35   $246.30  
  Purchase #5 $76.29   8.535%   $82.8014   $82.80   $82.80   $82.80  
  Purchase #6 $34.73   4.423%   $36.2661   $36.27   $36.25   $36.30  
  Purchase #7 $242.92   3.716%   $251.9469   $251.95   $251.95   $251.90  
  7 purchase totals = $866.61       $925.0153   $925.02   $925.00   $924.90