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	$111.31	9.208%	$121.5594	$121.56	$121.55	$121.60
Purchase #2	$184.56	6.578%	$196.7004	$196.70	$196.70	$196.70
Purchase #3	$47.36	13.304%	$53.6608	$53.66	$53.65	$53.70
Purchase #4	$153.82	7.564%	$165.4549	$165.45	$165.45	$165.50
Purchase #5	$104.67	12.433%	$117.6836	$117.68	$117.70	$117.70
Purchase #6	$124.36	3.355%	$128.5323	$128.53	$128.55	$128.50
Purchase #7	$131.39	10.192%	$144.7813	$144.78	$144.80	$144.80
7 purchase totals =	$857.47		$928.3727	$928.36	$928.40	$928.50