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	$88.62	13.516%	$100.5979	$100.60	$100.60	$100.60
Purchase #2	$139.32	6.852%	$148.8662	$148.87	$148.85	$148.90
Purchase #3	$161.25	4.198%	$168.0193	$168.02	$168.00	$168.00
Purchase #4	$85.99	3.762%	$89.2249	$89.22	$89.20	$89.20
Purchase #5	$243.86	12.252%	$273.7377	$273.74	$273.75	$273.70
Purchase #6	$73.58	10.292%	$81.1529	$81.15	$81.15	$81.20
Purchase #7	$247.41	4.643%	$258.8972	$258.90	$258.90	$258.90
7 purchase totals =	$1,040.03		$1,120.4961	$1,120.50	$1,120.45	$1,120.50