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	$148.48	7.580%	$159.7348	$159.73	$159.75	$159.70
Purchase #2	$110.88	5.800%	$117.311	$117.31	$117.30	$117.30
Purchase #3	$112.27	13.558%	$127.4916	$127.49	$127.50	$127.50
Purchase #4	$38.97	6.331%	$41.4372	$41.44	$41.45	$41.40
Purchase #5	$127.36	13.339%	$144.3486	$144.35	$144.35	$144.30
Purchase #6	$51.52	6.493%	$54.8652	$54.87	$54.85	$54.90
Purchase #7	$47.64	7.167%	$51.0544	$51.05	$51.05	$51.10
7 purchase totals =	$637.12		$696.2428	$696.24	$696.25	$696.20