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	$61.64	12.103%	$69.1003	$69.10	$69.10	$69.10
Purchase #2	$120.38	5.762%	$127.3163	$127.32	$127.30	$127.30
Purchase #3	$143.46	3.564%	$148.5729	$148.57	$148.55	$148.60
Purchase #4	$78.76	11.271%	$87.637	$87.64	$87.65	$87.60
Purchase #5	$91.47	13.366%	$103.6959	$103.70	$103.70	$103.70
Purchase #6	$151.48	5.640%	$160.0235	$160.02	$160.00	$160.00
Purchase #7	$173.90	12.802%	$196.1627	$196.16	$196.15	$196.20
7 purchase totals =	$821.09		$892.5086	$892.51	$892.45	$892.50