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	$57.31	13.593%	$65.1001	$65.10	$65.10	$65.10
Purchase #2	$94.25	11.634%	$105.215	$105.22	$105.20	$105.20
Purchase #3	$197.79	6.593%	$210.8303	$210.83	$210.85	$210.80
Purchase #4	$191.55	11.665%	$213.8943	$213.89	$213.90	$213.90
Purchase #5	$34.73	4.480%	$36.2859	$36.29	$36.30	$36.30
Purchase #6	$73.96	12.799%	$83.4261	$83.43	$83.45	$83.40
Purchase #7	$233.50	9.135%	$254.8302	$254.83	$254.85	$254.80
7 purchase totals =	$883.09		$969.5819	$969.59	$969.65	$969.50