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	$56.74	13.688%	$64.5066	$64.51	$64.50	$64.50
Purchase #2	$246.73	4.319%	$257.3863	$257.39	$257.40	$257.40
Purchase #3	$129.87	12.199%	$145.7128	$145.71	$145.70	$145.70
Purchase #4	$225.88	3.407%	$233.5757	$233.58	$233.60	$233.60
Purchase #5	$127.33	10.320%	$140.4705	$140.47	$140.45	$140.50
Purchase #6	$52.56	13.306%	$59.5536	$59.55	$59.55	$59.60
Purchase #7	$72.75	8.859%	$79.1949	$79.19	$79.20	$79.20
7 purchase totals =	$911.86		$980.4004	$980.40	$980.40	$980.50