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	$111.70	13.334%	$126.5941	$126.59	$126.60	$126.60
Purchase #2	$88.78	8.404%	$96.2411	$96.24	$96.25	$96.20
Purchase #3	$28.46	13.733%	$32.3684	$32.37	$32.35	$32.40
Purchase #4	$37.31	6.803%	$39.8482	$39.85	$39.85	$39.80
Purchase #5	$111.32	8.844%	$121.1651	$121.17	$121.15	$121.20
Purchase #6	$114.70	13.595%	$130.2935	$130.29	$130.30	$130.30
Purchase #7	$101.56	11.322%	$113.0586	$113.06	$113.05	$113.10
7 purchase totals =	$593.83		$659.5690	$659.57	$659.55	$659.60