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	$135.45	12.438%	$152.2973	$152.30	$152.30	$152.30
Purchase #2	$100.31	10.786%	$111.1294	$111.13	$111.15	$111.10
Purchase #3	$63.77	13.735%	$72.5288	$72.53	$72.55	$72.50
Purchase #4	$58.88	8.241%	$63.7323	$63.73	$63.75	$63.70
Purchase #5	$229.30	8.242%	$248.1989	$248.20	$248.20	$248.20
Purchase #6	$135.60	11.650%	$151.3974	$151.40	$151.40	$151.40
Purchase #7	$60.28	3.153%	$62.1806	$62.18	$62.20	$62.20
7 purchase totals =	$783.59		$861.4647	$861.47	$861.55	$861.40