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	$80.28	11.783%	$89.7394	$89.74	$89.75	$89.70
Purchase #2	$236.32	9.653%	$259.132	$259.13	$259.15	$259.10
Purchase #3	$13.68	12.821%	$15.4339	$15.43	$15.45	$15.40
Purchase #4	$160.75	12.741%	$181.2312	$181.23	$181.25	$181.20
Purchase #5	$172.29	13.149%	$194.9444	$194.94	$194.95	$194.90
Purchase #6	$130.25	13.160%	$147.3909	$147.39	$147.40	$147.40
Purchase #7	$205.94	5.722%	$217.7239	$217.72	$217.70	$217.70
7 purchase totals =	$999.51		$1,105.5957	$1,105.58	$1,105.65	$1,105.40