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	$56.79	4.738%	$59.4807	$59.48	$59.50	$59.50
Purchase #2	$80.65	5.485%	$85.0737	$85.07	$85.05	$85.10
Purchase #3	$92.77	4.125%	$96.5968	$96.60	$96.60	$96.60
Purchase #4	$148.88	7.357%	$159.8331	$159.83	$159.85	$159.80
Purchase #5	$107.57	10.346%	$118.6992	$118.70	$118.70	$118.70
Purchase #6	$88.44	12.683%	$99.6568	$99.66	$99.65	$99.70
Purchase #7	$18.40	13.846%	$20.9477	$20.95	$20.95	$20.90
7 purchase totals =	$593.50		$640.2880	$640.29	$640.30	$640.30