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	$82.43	8.793%	$89.6781	$89.68	$89.70	$89.70
Purchase #2	$245.76	12.426%	$276.2981	$276.30	$276.30	$276.30
Purchase #3	$137.86	6.210%	$146.4211	$146.42	$146.40	$146.40
Purchase #4	$208.86	10.858%	$231.538	$231.54	$231.55	$231.50
Purchase #5	$188.66	13.786%	$214.6687	$214.67	$214.65	$214.70
Purchase #6	$189.81	10.396%	$209.5426	$209.54	$209.55	$209.50
Purchase #7	$83.61	5.874%	$88.5213	$88.52	$88.50	$88.50
7 purchase totals =	$1,136.99		$1,256.6679	$1,256.67	$1,256.65	$1,256.60