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	$107.92	3.593%	$111.7976	$111.80	$111.80	$111.80
Purchase #2	$158.63	7.655%	$170.7731	$170.77	$170.75	$170.80
Purchase #3	$40.94	9.419%	$44.7961	$44.80	$44.80	$44.80
Purchase #4	$140.35	5.564%	$148.1591	$148.16	$148.15	$148.20
Purchase #5	$18.91	13.314%	$21.4277	$21.43	$21.45	$21.40
Purchase #6	$184.91	11.861%	$206.8422	$206.84	$206.85	$206.80
Purchase #7	$147.45	11.565%	$164.5026	$164.50	$164.50	$164.50
7 purchase totals =	$799.11		$868.2984	$868.30	$868.30	$868.30