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	$217.44	8.306%	$235.5006	$235.50	$235.50	$235.50
Purchase #2	$183.65	4.462%	$191.8445	$191.84	$191.85	$191.80
Purchase #3	$159.43	4.240%	$166.1898	$166.19	$166.20	$166.20
Purchase #4	$10.28	12.277%	$11.5421	$11.54	$11.55	$11.50
Purchase #5	$144.51	4.175%	$150.5433	$150.54	$150.55	$150.50
Purchase #6	$25.25	12.766%	$28.4734	$28.47	$28.45	$28.50
Purchase #7	$81.76	9.102%	$89.2018	$89.20	$89.20	$89.20
7 purchase totals =	$822.32		$873.2955	$873.28	$873.30	$873.20