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	$139.73	13.311%	$158.3295	$158.33	$158.35	$158.30
Purchase #2	$155.90	10.398%	$172.1105	$172.11	$172.10	$172.10
Purchase #3	$233.42	11.344%	$259.8992	$259.90	$259.90	$259.90
Purchase #4	$126.50	3.643%	$131.1084	$131.11	$131.10	$131.10
Purchase #5	$249.87	8.210%	$270.3843	$270.38	$270.40	$270.40
Purchase #6	$71.52	12.814%	$80.6846	$80.68	$80.70	$80.70
Purchase #7	$106.40	4.760%	$111.4646	$111.46	$111.45	$111.50
7 purchase totals =	$1,083.34		$1,183.9811	$1,183.97	$1,184.00	$1,184.00