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	$144.79	13.821%	$164.8014	$164.80	$164.80	$164.80
Purchase #2	$189.77	9.817%	$208.3997	$208.40	$208.40	$208.40
Purchase #3	$104.35	6.564%	$111.1995	$111.20	$111.20	$111.20
Purchase #4	$32.61	11.269%	$36.2848	$36.28	$36.30	$36.30
Purchase #5	$129.84	8.150%	$140.422	$140.42	$140.40	$140.40
Purchase #6	$57.47	6.393%	$61.1441	$61.14	$61.15	$61.10
Purchase #7	$143.91	4.566%	$150.4809	$150.48	$150.50	$150.50
7 purchase totals =	$802.74		$872.7324	$872.72	$872.75	$872.70