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	$169.61	9.383%	$185.5245	$185.52	$185.50	$185.50
Purchase #2	$131.30	11.872%	$146.8879	$146.89	$146.90	$146.90
Purchase #3	$172.57	6.381%	$183.5817	$183.58	$183.60	$183.60
Purchase #4	$100.92	5.460%	$106.4302	$106.43	$106.45	$106.40
Purchase #5	$195.75	8.331%	$212.0579	$212.06	$212.05	$212.10
Purchase #6	$189.27	6.125%	$200.8628	$200.86	$200.85	$200.90
Purchase #7	$237.49	7.333%	$254.9051	$254.91	$254.90	$254.90
7 purchase totals =	$1,196.91		$1,290.2501	$1,290.25	$1,290.25	$1,290.30