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	$223.47	6.676%	$238.3889	$238.39	$238.40	$238.40
Purchase #2	$191.95	11.643%	$214.2987	$214.30	$214.30	$214.30
Purchase #3	$83.27	7.603%	$89.601	$89.60	$89.60	$89.60
Purchase #4	$88.74	7.606%	$95.4896	$95.49	$95.50	$95.50
Purchase #5	$52.39	9.581%	$57.4095	$57.41	$57.40	$57.40
Purchase #6	$17.61	3.468%	$18.2207	$18.22	$18.20	$18.20
Purchase #7	$241.66	13.723%	$274.823	$274.82	$274.80	$274.80
7 purchase totals =	$899.09		$988.2314	$988.23	$988.20	$988.20