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	$166.46	8.206%	$180.1197	$180.12	$180.10	$180.10
Purchase #2	$11.92	3.669%	$12.3573	$12.36	$12.35	$12.40
Purchase #3	$138.78	9.660%	$152.1861	$152.19	$152.20	$152.20
Purchase #4	$100.63	5.609%	$106.2743	$106.27	$106.25	$106.30
Purchase #5	$132.52	7.536%	$142.5067	$142.51	$142.50	$142.50
Purchase #6	$68.35	6.136%	$72.544	$72.54	$72.55	$72.50
Purchase #7	$57.79	6.379%	$61.4764	$61.48	$61.50	$61.50
7 purchase totals =	$676.45		$727.4645	$727.47	$727.45	$727.50