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	$130.53	11.193%	$145.1402	$145.14	$145.15	$145.10
Purchase #2	$239.60	6.493%	$255.1572	$255.16	$255.15	$255.20
Purchase #3	$86.45	3.642%	$89.5985	$89.60	$89.60	$89.60
Purchase #4	$147.25	9.685%	$161.5112	$161.51	$161.50	$161.50
Purchase #5	$26.27	6.864%	$28.0732	$28.07	$28.05	$28.10
Purchase #6	$44.40	11.554%	$49.53	$49.53	$49.55	$49.50
Purchase #7	$72.38	13.298%	$82.0051	$82.01	$82.00	$82.00
7 purchase totals =	$746.88		$811.0154	$811.02	$811.00	$811.00