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	$132.39	5.485%	$139.6516	$139.65	$139.65	$139.70
Purchase #2	$82.72	4.705%	$86.612	$86.61	$86.60	$86.60
Purchase #3	$48.89	10.487%	$54.0171	$54.02	$54.00	$54.00
Purchase #4	$6.61	13.671%	$7.5137	$7.51	$7.50	$7.50
Purchase #5	$227.72	12.607%	$256.4287	$256.43	$256.45	$256.40
Purchase #6	$71.46	4.191%	$74.4549	$74.45	$74.45	$74.50
Purchase #7	$89.41	10.803%	$99.069	$99.07	$99.05	$99.10
7 purchase totals =	$659.20		$717.7470	$717.74	$717.70	$717.80