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	$37.39	8.565%	$40.5925	$40.59	$40.60	$40.60
Purchase #2	$94.74	7.733%	$102.0662	$102.07	$102.05	$102.10
Purchase #3	$94.43	4.414%	$98.5981	$98.60	$98.60	$98.60
Purchase #4	$245.64	3.427%	$254.0581	$254.06	$254.05	$254.10
Purchase #5	$164.57	4.580%	$172.1073	$172.11	$172.10	$172.10
Purchase #6	$93.55	7.339%	$100.4156	$100.42	$100.40	$100.40
Purchase #7	$18.85	7.848%	$20.3293	$20.33	$20.35	$20.30
7 purchase totals =	$749.17		$788.1671	$788.18	$788.15	$788.20