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	$171.30	11.727%	$191.3884	$191.39	$191.40	$191.40
Purchase #2	$157.90	7.869%	$170.3252	$170.33	$170.35	$170.30
Purchase #3	$224.43	13.365%	$254.4251	$254.43	$254.45	$254.40
Purchase #4	$224.69	7.547%	$241.6474	$241.65	$241.65	$241.60
Purchase #5	$148.94	7.321%	$159.8439	$159.84	$159.85	$159.80
Purchase #6	$33.33	13.733%	$37.9072	$37.91	$37.90	$37.90
Purchase #7	$204.55	7.495%	$219.881	$219.88	$219.90	$219.90
7 purchase totals =	$1,165.14		$1,275.4182	$1,275.43	$1,275.50	$1,275.30