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	$114.36	12.572%	$128.7373	$128.74	$128.75	$128.70
Purchase #2	$147.72	8.631%	$160.4697	$160.47	$160.45	$160.50
Purchase #3	$155.26	11.439%	$173.0202	$173.02	$173.00	$173.00
Purchase #4	$112.45	10.170%	$123.8862	$123.89	$123.90	$123.90
Purchase #5	$81.64	9.720%	$89.5754	$89.58	$89.60	$89.60
Purchase #6	$43.75	13.140%	$49.4988	$49.50	$49.50	$49.50
Purchase #7	$126.47	8.575%	$137.3148	$137.31	$137.30	$137.30
7 purchase totals =	$781.65		$862.5024	$862.51	$862.50	$862.50