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	$145.27	8.490%	$157.6034	$157.60	$157.60	$157.60
Purchase #2	$31.73	8.310%	$34.3668	$34.37	$34.35	$34.40
Purchase #3	$34.98	7.191%	$37.4954	$37.50	$37.50	$37.50
Purchase #4	$88.46	12.123%	$99.184	$99.18	$99.20	$99.20
Purchase #5	$42.65	7.120%	$45.6867	$45.69	$45.70	$45.70
Purchase #6	$44.28	9.684%	$48.5681	$48.57	$48.55	$48.60
Purchase #7	$116.82	3.485%	$120.8912	$120.89	$120.90	$120.90
7 purchase totals =	$504.19		$543.7956	$543.80	$543.80	$543.90