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	$245.45	12.636%	$276.4651	$276.47	$276.45	$276.50
Purchase #2	$217.89	12.244%	$244.5685	$244.57	$244.55	$244.60
Purchase #3	$165.56	8.503%	$179.6376	$179.64	$179.65	$179.60
Purchase #4	$128.71	12.122%	$144.3122	$144.31	$144.30	$144.30
Purchase #5	$53.81	4.769%	$56.3762	$56.38	$56.40	$56.40
Purchase #6	$77.81	3.613%	$80.6213	$80.62	$80.60	$80.60
Purchase #7	$71.86	12.202%	$80.6284	$80.63	$80.65	$80.60
7 purchase totals =	$961.09		$1,062.6093	$1,062.62	$1,062.60	$1,062.60