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	$42.27	8.609%	$45.909	$45.91	$45.90	$45.90
Purchase #2	$200.62	10.238%	$221.1595	$221.16	$221.15	$221.20
Purchase #3	$146.86	4.673%	$153.7228	$153.72	$153.70	$153.70
Purchase #4	$206.27	13.372%	$233.8524	$233.85	$233.85	$233.90
Purchase #5	$215.73	13.212%	$244.2322	$244.23	$244.25	$244.20
Purchase #6	$150.60	10.336%	$166.166	$166.17	$166.15	$166.20
Purchase #7	$212.75	4.519%	$222.3642	$222.36	$222.35	$222.40
7 purchase totals =	$1,175.10		$1,287.4061	$1,287.40	$1,287.35	$1,287.50