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	$130.75	12.150%	$146.6361	$146.64	$146.65	$146.60
Purchase #2	$204.27	11.661%	$228.0899	$228.09	$228.10	$228.10
Purchase #3	$53.27	4.271%	$55.5452	$55.55	$55.55	$55.50
Purchase #4	$86.72	3.171%	$89.4699	$89.47	$89.45	$89.50
Purchase #5	$38.40	6.439%	$40.8726	$40.87	$40.85	$40.90
Purchase #6	$244.34	13.229%	$276.6637	$276.66	$276.65	$276.70
Purchase #7	$16.32	12.543%	$18.367	$18.37	$18.35	$18.40
7 purchase totals =	$774.07		$855.6444	$855.65	$855.60	$855.70