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	$182.85	9.253%	$199.7691	$199.77	$199.75	$199.80
Purchase #2	$188.40	5.590%	$198.9316	$198.93	$198.95	$198.90
Purchase #3	$80.58	11.808%	$90.0949	$90.09	$90.10	$90.10
Purchase #4	$84.72	7.785%	$91.3155	$91.32	$91.30	$91.30
Purchase #5	$11.81	4.182%	$12.3039	$12.30	$12.30	$12.30
Purchase #6	$64.25	3.183%	$66.2951	$66.30	$66.30	$66.30
Purchase #7	$243.72	11.295%	$271.2482	$271.25	$271.25	$271.20
7 purchase totals =	$856.33		$929.9583	$929.96	$929.95	$929.90