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	$126.80	3.710%	$131.5043	$131.50	$131.50	$131.50
Purchase #2	$63.70	11.848%	$71.2472	$71.25	$71.25	$71.20
Purchase #3	$27.84	12.565%	$31.3381	$31.34	$31.35	$31.30
Purchase #4	$59.28	9.720%	$65.042	$65.04	$65.05	$65.00
Purchase #5	$99.41	8.488%	$107.8479	$107.85	$107.85	$107.80
Purchase #6	$157.56	9.718%	$172.8717	$172.87	$172.85	$172.90
Purchase #7	$98.80	13.162%	$111.8041	$111.80	$111.80	$111.80
7 purchase totals =	$633.39		$691.6553	$691.65	$691.65	$691.50