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	$131.45	4.406%	$137.2417	$137.24	$137.25	$137.20
Purchase #2	$139.72	7.843%	$150.6782	$150.68	$150.70	$150.70
Purchase #3	$240.35	11.655%	$268.3628	$268.36	$268.35	$268.40
Purchase #4	$102.74	8.198%	$111.1626	$111.16	$111.15	$111.20
Purchase #5	$224.77	8.771%	$244.4846	$244.48	$244.50	$244.50
Purchase #6	$14.53	12.142%	$16.2942	$16.29	$16.30	$16.30
Purchase #7	$40.83	3.408%	$42.2215	$42.22	$42.20	$42.20
7 purchase totals =	$894.39		$970.4456	$970.43	$970.45	$970.50