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	$210.72	13.287%	$238.7184	$238.72	$238.70	$238.70
Purchase #2	$90.31	9.627%	$99.0041	$99.00	$99.00	$99.00
Purchase #3	$95.76	7.714%	$103.1469	$103.15	$103.15	$103.10
Purchase #4	$129.25	13.223%	$146.3407	$146.34	$146.35	$146.30
Purchase #5	$44.93	11.398%	$50.0511	$50.05	$50.05	$50.10
Purchase #6	$229.85	11.871%	$257.1355	$257.14	$257.15	$257.10
Purchase #7	$16.25	4.778%	$17.0264	$17.03	$17.05	$17.00
7 purchase totals =	$817.07		$911.4231	$911.43	$911.45	$911.30