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	$100.27	8.428%	$108.7208	$108.72	$108.70	$108.70
Purchase #2	$235.95	9.530%	$258.436	$258.44	$258.45	$258.40
Purchase #3	$6.78	7.450%	$7.2851	$7.29	$7.30	$7.30
Purchase #4	$33.82	11.191%	$37.6048	$37.60	$37.60	$37.60
Purchase #5	$217.73	12.799%	$245.5973	$245.60	$245.60	$245.60
Purchase #6	$20.41	10.298%	$22.5118	$22.51	$22.50	$22.50
Purchase #7	$33.75	7.365%	$36.2357	$36.24	$36.25	$36.20
7 purchase totals =	$648.71		$716.3915	$716.40	$716.40	$716.30