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	$18.34	10.550%	$20.2749	$20.27	$20.25	$20.30
Purchase #2	$147.43	9.261%	$161.0835	$161.08	$161.10	$161.10
Purchase #3	$63.98	13.773%	$72.792	$72.79	$72.80	$72.80
Purchase #4	$42.47	6.572%	$45.2611	$45.26	$45.25	$45.30
Purchase #5	$17.74	13.157%	$20.0741	$20.07	$20.05	$20.10
Purchase #6	$196.54	11.460%	$219.0635	$219.06	$219.05	$219.10
Purchase #7	$132.38	9.294%	$144.6834	$144.68	$144.70	$144.70
7 purchase totals =	$618.88		$683.2325	$683.21	$683.20	$683.40