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	$165.35	5.396%	$174.2723	$174.27	$174.25	$174.30
Purchase #2	$139.46	6.447%	$148.451	$148.45	$148.45	$148.50
Purchase #3	$89.33	7.379%	$95.9217	$95.92	$95.90	$95.90
Purchase #4	$35.52	13.178%	$40.2008	$40.20	$40.20	$40.20
Purchase #5	$73.40	6.732%	$78.3413	$78.34	$78.35	$78.30
Purchase #6	$9.77	3.145%	$10.0773	$10.08	$10.10	$10.10
Purchase #7	$244.70	6.423%	$260.4171	$260.42	$260.40	$260.40
7 purchase totals =	$757.53		$807.6815	$807.68	$807.65	$807.70