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	$44.88	8.374%	$48.6383	$48.64	$48.65	$48.60
Purchase #2	$151.79	10.536%	$167.7826	$167.78	$167.80	$167.80
Purchase #3	$148.96	6.463%	$158.5873	$158.59	$158.60	$158.60
Purchase #4	$33.46	4.466%	$34.9543	$34.95	$34.95	$35.00
Purchase #5	$12.79	8.801%	$13.9156	$13.92	$13.90	$13.90
Purchase #6	$235.61	4.337%	$245.8284	$245.83	$245.85	$245.80
Purchase #7	$19.64	9.570%	$21.5195	$21.52	$21.50	$21.50
7 purchase totals =	$647.13		$691.2260	$691.23	$691.25	$691.20