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	$140.54	11.828%	$157.1631	$157.16	$157.15	$157.20
Purchase #2	$26.48	11.436%	$29.5083	$29.51	$29.50	$29.50
Purchase #3	$231.37	13.605%	$262.8479	$262.85	$262.85	$262.80
Purchase #4	$10.36	12.518%	$11.6569	$11.66	$11.65	$11.70
Purchase #5	$75.55	4.117%	$78.6604	$78.66	$78.65	$78.70
Purchase #6	$85.82	4.595%	$89.7634	$89.76	$89.75	$89.80
Purchase #7	$16.28	7.333%	$17.4738	$17.47	$17.45	$17.50
7 purchase totals =	$586.40		$647.0738	$647.07	$647.00	$647.20