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	$123.42	11.107%	$137.1283	$137.13	$137.15	$137.10
Purchase #2	$27.91	10.463%	$30.8302	$30.83	$30.85	$30.80
Purchase #3	$126.72	13.512%	$143.8424	$143.84	$143.85	$143.80
Purchase #4	$43.48	7.173%	$46.5988	$46.60	$46.60	$46.60
Purchase #5	$227.27	12.491%	$255.6583	$255.66	$255.65	$255.70
Purchase #6	$129.35	7.482%	$139.028	$139.03	$139.05	$139.00
Purchase #7	$137.62	13.582%	$156.3115	$156.31	$156.30	$156.30
7 purchase totals =	$815.77		$909.3975	$909.40	$909.45	$909.30