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	$158.41	7.589%	$170.4317	$170.43	$170.45	$170.40
Purchase #2	$58.57	7.465%	$62.9423	$62.94	$62.95	$62.90
Purchase #3	$116.31	8.318%	$125.9847	$125.98	$126.00	$126.00
Purchase #4	$79.70	13.401%	$90.3806	$90.38	$90.40	$90.40
Purchase #5	$129.83	12.240%	$145.7212	$145.72	$145.70	$145.70
Purchase #6	$65.74	12.333%	$73.8477	$73.85	$73.85	$73.80
Purchase #7	$63.70	13.622%	$72.3772	$72.38	$72.40	$72.40
7 purchase totals =	$672.26		$741.6854	$741.68	$741.75	$741.60