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	$57.91	5.834%	$61.2885	$61.29	$61.30	$61.30
Purchase #2	$49.72	11.211%	$55.2941	$55.29	$55.30	$55.30
Purchase #3	$226.27	7.342%	$242.8827	$242.88	$242.90	$242.90
Purchase #4	$236.74	7.843%	$255.3075	$255.31	$255.30	$255.30
Purchase #5	$138.72	8.863%	$151.0148	$151.01	$151.00	$151.00
Purchase #6	$101.43	3.642%	$105.1241	$105.12	$105.10	$105.10
Purchase #7	$59.39	5.223%	$62.4919	$62.49	$62.50	$62.50
7 purchase totals =	$870.18		$933.4036	$933.39	$933.40	$933.40