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	$41.90	13.102%	$47.3897	$47.39	$47.40	$47.40
Purchase #2	$92.89	7.143%	$99.5251	$99.53	$99.55	$99.50
Purchase #3	$38.77	12.287%	$43.5337	$43.53	$43.55	$43.50
Purchase #4	$202.86	8.863%	$220.8395	$220.84	$220.85	$220.80
Purchase #5	$25.50	11.348%	$28.3937	$28.39	$28.40	$28.40
Purchase #6	$155.78	13.500%	$176.8103	$176.81	$176.80	$176.80
Purchase #7	$166.85	7.230%	$178.9133	$178.91	$178.90	$178.90
7 purchase totals =	$724.55		$795.4053	$795.40	$795.45	$795.30