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	$234.88	5.389%	$247.5377	$247.54	$247.55	$247.50
Purchase #2	$95.50	6.107%	$101.3322	$101.33	$101.35	$101.30
Purchase #3	$155.95	10.689%	$172.6195	$172.62	$172.60	$172.60
Purchase #4	$72.30	8.504%	$78.4484	$78.45	$78.45	$78.40
Purchase #5	$27.41	11.286%	$30.5035	$30.50	$30.50	$30.50
Purchase #6	$89.56	5.850%	$94.7993	$94.80	$94.80	$94.80
Purchase #7	$201.37	12.355%	$226.2493	$226.25	$226.25	$226.20
7 purchase totals =	$876.97		$951.4899	$951.49	$951.50	$951.30