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	$246.52	10.697%	$272.8902	$272.89	$272.90	$272.90
Purchase #2	$10.35	11.369%	$11.5267	$11.53	$11.55	$11.50
Purchase #3	$49.37	7.662%	$53.1527	$53.15	$53.15	$53.20
Purchase #4	$85.63	6.414%	$91.1223	$91.12	$91.10	$91.10
Purchase #5	$65.33	13.863%	$74.3867	$74.39	$74.40	$74.40
Purchase #6	$93.94	7.382%	$100.8747	$100.87	$100.85	$100.90
Purchase #7	$27.33	9.406%	$29.9007	$29.90	$29.90	$29.90
7 purchase totals =	$578.47		$633.8540	$633.85	$633.85	$633.90