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	$217.42	11.536%	$242.5016	$242.50	$242.50	$242.50
Purchase #2	$176.95	13.242%	$200.3817	$200.38	$200.40	$200.40
Purchase #3	$61.53	6.321%	$65.4193	$65.42	$65.40	$65.40
Purchase #4	$172.42	4.166%	$179.603	$179.60	$179.60	$179.60
Purchase #5	$62.96	13.521%	$71.4728	$71.47	$71.45	$71.50
Purchase #6	$32.57	13.343%	$36.9158	$36.92	$36.90	$36.90
Purchase #7	$130.72	11.525%	$145.7855	$145.79	$145.80	$145.80
7 purchase totals =	$854.57		$942.0797	$942.08	$942.05	$942.10