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	$71.91	13.335%	$81.4992	$81.50	$81.50	$81.50
Purchase #2	$146.76	7.504%	$157.7729	$157.77	$157.75	$157.80
Purchase #3	$188.66	12.234%	$211.7407	$211.74	$211.75	$211.70
Purchase #4	$36.40	11.868%	$40.72	$40.72	$40.70	$40.70
Purchase #5	$146.99	12.242%	$164.9845	$164.98	$165.00	$165.00
Purchase #6	$67.82	5.830%	$71.7739	$71.77	$71.75	$71.80
Purchase #7	$112.59	12.845%	$127.0522	$127.05	$127.05	$127.10
7 purchase totals =	$771.13		$855.5434	$855.53	$855.50	$855.60