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	$16.40	11.403%	$18.2701	$18.27	$18.25	$18.30
Purchase #2	$218.29	11.586%	$243.5811	$243.58	$243.60	$243.60
Purchase #3	$60.95	8.108%	$65.8918	$65.89	$65.90	$65.90
Purchase #4	$44.88	3.369%	$46.392	$46.39	$46.40	$46.40
Purchase #5	$151.91	12.165%	$170.3899	$170.39	$170.40	$170.40
Purchase #6	$14.51	6.141%	$15.4011	$15.40	$15.40	$15.40
Purchase #7	$115.52	10.386%	$127.5179	$127.52	$127.50	$127.50
7 purchase totals =	$622.46		$687.4439	$687.44	$687.45	$687.50