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	$55.40	3.570%	$57.3778	$57.38	$57.40	$57.40
Purchase #2	$119.26	6.826%	$127.4007	$127.40	$127.40	$127.40
Purchase #3	$77.53	13.552%	$88.0369	$88.04	$88.05	$88.00
Purchase #4	$98.64	12.870%	$111.335	$111.34	$111.35	$111.30
Purchase #5	$87.76	4.420%	$91.639	$91.64	$91.65	$91.60
Purchase #6	$154.45	12.135%	$173.1925	$173.19	$173.20	$173.20
Purchase #7	$210.29	4.593%	$219.9486	$219.95	$219.95	$219.90
7 purchase totals =	$803.33		$868.9305	$868.94	$869.00	$868.80