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	$22.75	7.703%	$24.5024	$24.50	$24.50	$24.50
Purchase #2	$136.59	6.611%	$145.62	$145.62	$145.60	$145.60
Purchase #3	$147.37	4.835%	$154.4953	$154.50	$154.50	$154.50
Purchase #4	$76.69	4.846%	$80.4064	$80.41	$80.40	$80.40
Purchase #5	$33.68	10.597%	$37.2491	$37.25	$37.25	$37.20
Purchase #6	$28.80	13.520%	$32.6938	$32.69	$32.70	$32.70
Purchase #7	$34.58	7.644%	$37.2233	$37.22	$37.20	$37.20
7 purchase totals =	$480.46		$512.1903	$512.19	$512.15	$512.10