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	$68.49	10.822%	$75.902	$75.90	$75.90	$75.90
Purchase #2	$248.63	5.593%	$262.5359	$262.54	$262.55	$262.50
Purchase #3	$86.33	4.598%	$90.2995	$90.30	$90.30	$90.30
Purchase #4	$49.83	5.371%	$52.5064	$52.51	$52.50	$52.50
Purchase #5	$67.35	10.119%	$74.1651	$74.17	$74.15	$74.20
Purchase #6	$83.36	9.471%	$91.255	$91.26	$91.25	$91.30
Purchase #7	$146.70	9.388%	$160.4722	$160.47	$160.45	$160.50
7 purchase totals =	$750.69		$807.1361	$807.15	$807.10	$807.20