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	$83.47	10.813%	$92.4956	$92.50	$92.50	$92.50
Purchase #2	$42.62	7.379%	$45.7649	$45.76	$45.75	$45.80
Purchase #3	$141.91	6.487%	$151.1157	$151.12	$151.10	$151.10
Purchase #4	$9.76	7.112%	$10.4541	$10.45	$10.45	$10.50
Purchase #5	$129.74	11.635%	$144.8352	$144.84	$144.85	$144.80
Purchase #6	$183.93	13.581%	$208.9095	$208.91	$208.90	$208.90
Purchase #7	$134.64	5.135%	$141.5538	$141.55	$141.55	$141.60
7 purchase totals =	$726.07		$795.1288	$795.13	$795.10	$795.20