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	$149.60	5.296%	$157.5228	$157.52	$157.50	$157.50
Purchase #2	$175.94	11.683%	$196.4951	$196.50	$196.50	$196.50
Purchase #3	$162.29	10.809%	$179.8319	$179.83	$179.85	$179.80
Purchase #4	$7.92	6.353%	$8.4232	$8.42	$8.40	$8.40
Purchase #5	$162.66	5.724%	$171.9707	$171.97	$171.95	$172.00
Purchase #6	$47.33	12.579%	$53.2836	$53.28	$53.30	$53.30
Purchase #7	$55.79	3.464%	$57.7226	$57.72	$57.70	$57.70
7 purchase totals =	$761.53		$825.2499	$825.24	$825.20	$825.20