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	$140.40	12.822%	$158.4021	$158.40	$158.40	$158.40
Purchase #2	$18.94	9.322%	$20.7056	$20.71	$20.70	$20.70
Purchase #3	$240.59	4.603%	$251.6644	$251.66	$251.65	$251.70
Purchase #4	$134.28	8.179%	$145.2628	$145.26	$145.25	$145.30
Purchase #5	$25.42	11.404%	$28.3189	$28.32	$28.30	$28.30
Purchase #6	$152.65	5.175%	$160.5496	$160.55	$160.55	$160.50
Purchase #7	$62.78	13.363%	$71.1693	$71.17	$71.15	$71.20
7 purchase totals =	$775.06		$836.0727	$836.07	$836.00	$836.10