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	$33.70	3.733%	$34.958	$34.96	$34.95	$35.00
Purchase #2	$56.91	4.425%	$59.4283	$59.43	$59.45	$59.40
Purchase #3	$52.35	6.201%	$55.5962	$55.60	$55.60	$55.60
Purchase #4	$59.95	11.490%	$66.8383	$66.84	$66.85	$66.80
Purchase #5	$195.74	13.770%	$222.6934	$222.69	$222.70	$222.70
Purchase #6	$82.90	6.575%	$88.3507	$88.35	$88.35	$88.40
Purchase #7	$135.97	12.747%	$153.3021	$153.30	$153.30	$153.30
7 purchase totals =	$617.52		$681.1670	$681.17	$681.20	$681.20