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	$245.90	13.659%	$279.4875	$279.49	$279.50	$279.50
Purchase #2	$126.32	3.656%	$130.9383	$130.94	$130.95	$130.90
Purchase #3	$26.33	13.831%	$29.9717	$29.97	$29.95	$30.00
Purchase #4	$189.46	5.231%	$199.3707	$199.37	$199.35	$199.40
Purchase #5	$100.53	10.541%	$111.1269	$111.13	$111.15	$111.10
Purchase #6	$91.80	7.244%	$98.45	$98.45	$98.45	$98.50
Purchase #7	$172.63	13.434%	$195.8211	$195.82	$195.80	$195.80
7 purchase totals =	$952.97		$1,045.1662	$1,045.17	$1,045.15	$1,045.20