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	$16.52	7.446%	$17.7501	$17.75	$17.75	$17.80
Purchase #2	$69.51	6.299%	$73.8884	$73.89	$73.90	$73.90
Purchase #3	$123.40	5.535%	$130.2302	$130.23	$130.25	$130.20
Purchase #4	$12.66	4.818%	$13.27	$13.27	$13.25	$13.30
Purchase #5	$11.32	11.255%	$12.5941	$12.59	$12.60	$12.60
Purchase #6	$10.87	12.667%	$12.2469	$12.25	$12.25	$12.20
Purchase #7	$137.32	6.463%	$146.195	$146.20	$146.20	$146.20
7 purchase totals =	$381.60		$406.1747	$406.18	$406.20	$406.20