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	$34.70	7.312%	$37.2373	$37.24	$37.25	$37.20
Purchase #2	$173.38	11.274%	$192.9269	$192.93	$192.95	$192.90
Purchase #3	$195.84	8.691%	$212.8605	$212.86	$212.85	$212.90
Purchase #4	$236.27	7.562%	$254.1367	$254.14	$254.15	$254.10
Purchase #5	$28.86	12.379%	$32.4326	$32.43	$32.45	$32.40
Purchase #6	$239.84	13.338%	$271.8299	$271.83	$271.85	$271.80
Purchase #7	$11.30	5.180%	$11.8853	$11.89	$11.90	$11.90
7 purchase totals =	$920.19		$1,013.3092	$1,013.32	$1,013.40	$1,013.20