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	$7.26	11.164%	$8.0705	$8.07	$8.05	$8.10
Purchase #2	$104.86	9.228%	$114.5365	$114.54	$114.55	$114.50
Purchase #3	$238.57	8.325%	$258.431	$258.43	$258.45	$258.40
Purchase #4	$243.69	4.704%	$255.1532	$255.15	$255.15	$255.20
Purchase #5	$60.51	12.161%	$67.8686	$67.87	$67.85	$67.90
Purchase #6	$29.79	10.251%	$32.8438	$32.84	$32.85	$32.80
Purchase #7	$158.53	4.103%	$165.0345	$165.03	$165.05	$165.00
7 purchase totals =	$843.21		$901.9381	$901.93	$901.95	$901.90