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	$31.83	6.339%	$33.8477	$33.85	$33.85	$33.80
Purchase #2	$111.91	13.265%	$126.7549	$126.75	$126.75	$126.80
Purchase #3	$244.90	12.417%	$275.3092	$275.31	$275.30	$275.30
Purchase #4	$107.86	8.705%	$117.2492	$117.25	$117.25	$117.20
Purchase #5	$18.98	5.718%	$20.0653	$20.07	$20.05	$20.10
Purchase #6	$95.88	10.322%	$105.7767	$105.78	$105.80	$105.80
Purchase #7	$138.72	3.273%	$143.2603	$143.26	$143.25	$143.30
7 purchase totals =	$750.08		$822.2633	$822.27	$822.25	$822.30