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	$10.60	13.743%	$12.0568	$12.06	$12.05	$12.10
Purchase #2	$231.59	12.125%	$259.6703	$259.67	$259.65	$259.70
Purchase #3	$165.56	7.404%	$177.8181	$177.82	$177.80	$177.80
Purchase #4	$84.51	6.566%	$90.0589	$90.06	$90.05	$90.10
Purchase #5	$227.86	11.631%	$254.3624	$254.36	$254.35	$254.40
Purchase #6	$52.57	3.611%	$54.4683	$54.47	$54.45	$54.50
Purchase #7	$18.26	11.345%	$20.3316	$20.33	$20.35	$20.30
7 purchase totals =	$790.95		$868.7664	$868.77	$868.70	$868.90