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	$173.46	13.177%	$196.3168	$196.32	$196.30	$196.30
Purchase #2	$81.62	4.523%	$85.3117	$85.31	$85.30	$85.30
Purchase #3	$30.71	11.744%	$34.3166	$34.32	$34.30	$34.30
Purchase #4	$144.71	7.569%	$155.6631	$155.66	$155.65	$155.70
Purchase #5	$141.63	6.859%	$151.3444	$151.34	$151.35	$151.30
Purchase #6	$100.60	3.193%	$103.8122	$103.81	$103.80	$103.80
Purchase #7	$230.65	10.243%	$254.2755	$254.28	$254.30	$254.30
7 purchase totals =	$903.38		$981.0403	$981.04	$981.00	$981.00