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	$170.64	10.313%	$188.2381	$188.24	$188.25	$188.20
Purchase #2	$18.28	13.657%	$20.7765	$20.78	$20.80	$20.80
Purchase #3	$168.45	9.160%	$183.88	$183.88	$183.90	$183.90
Purchase #4	$34.72	10.196%	$38.2601	$38.26	$38.25	$38.30
Purchase #5	$247.82	10.256%	$273.2364	$273.24	$273.25	$273.20
Purchase #6	$199.28	11.810%	$222.815	$222.82	$222.80	$222.80
Purchase #7	$197.93	13.420%	$224.4922	$224.49	$224.50	$224.50
7 purchase totals =	$1,037.12		$1,151.6983	$1,151.71	$1,151.75	$1,151.70