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	$222.27	7.124%	$238.1045	$238.10	$238.10	$238.10
Purchase #2	$93.30	7.411%	$100.2145	$100.21	$100.20	$100.20
Purchase #3	$146.36	8.673%	$159.0538	$159.05	$159.05	$159.10
Purchase #4	$233.26	13.191%	$264.0293	$264.03	$264.05	$264.00
Purchase #5	$104.45	4.245%	$108.8839	$108.88	$108.90	$108.90
Purchase #6	$95.60	4.385%	$99.7921	$99.79	$99.80	$99.80
Purchase #7	$86.27	13.743%	$98.1261	$98.13	$98.15	$98.10
7 purchase totals =	$981.51		$1,068.2042	$1,068.19	$1,068.25	$1,068.20