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	$86.34	3.397%	$89.273	$89.27	$89.25	$89.30
Purchase #2	$18.65	10.104%	$20.5344	$20.53	$20.55	$20.50
Purchase #3	$95.29	5.169%	$100.2155	$100.22	$100.20	$100.20
Purchase #4	$182.27	3.623%	$188.8736	$188.87	$188.85	$188.90
Purchase #5	$61.30	11.370%	$68.2698	$68.27	$68.25	$68.30
Purchase #6	$177.39	4.522%	$185.4116	$185.41	$185.40	$185.40
Purchase #7	$159.64	10.722%	$176.7566	$176.76	$176.75	$176.80
7 purchase totals =	$780.88		$829.3345	$829.33	$829.25	$829.40