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	$88.92	6.158%	$94.3957	$94.40	$94.40	$94.40
Purchase #2	$77.72	10.324%	$85.7438	$85.74	$85.75	$85.70
Purchase #3	$244.75	8.573%	$265.7324	$265.73	$265.75	$265.70
Purchase #4	$85.95	4.155%	$89.5212	$89.52	$89.50	$89.50
Purchase #5	$127.44	8.321%	$138.0443	$138.04	$138.05	$138.00
Purchase #6	$99.94	10.601%	$110.5346	$110.53	$110.55	$110.50
Purchase #7	$23.50	8.846%	$25.5788	$25.58	$25.60	$25.60
7 purchase totals =	$748.22		$809.5508	$809.54	$809.60	$809.40