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	$146.96	12.779%	$165.74	$165.74	$165.75	$165.70
Purchase #2	$104.84	6.727%	$111.8926	$111.89	$111.90	$111.90
Purchase #3	$85.37	12.699%	$96.2111	$96.21	$96.20	$96.20
Purchase #4	$222.89	3.805%	$231.371	$231.37	$231.35	$231.40
Purchase #5	$54.41	10.513%	$60.1301	$60.13	$60.15	$60.10
Purchase #6	$92.53	10.408%	$102.1605	$102.16	$102.15	$102.20
Purchase #7	$98.72	6.784%	$105.4172	$105.42	$105.40	$105.40
7 purchase totals =	$805.72		$872.9225	$872.92	$872.90	$872.90