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	$148.45	6.755%	$158.4778	$158.48	$158.50	$158.50
Purchase #2	$121.62	5.673%	$128.5195	$128.52	$128.50	$128.50
Purchase #3	$161.41	13.870%	$183.7976	$183.80	$183.80	$183.80
Purchase #4	$59.50	9.672%	$65.2548	$65.25	$65.25	$65.30
Purchase #5	$159.85	8.391%	$173.263	$173.26	$173.25	$173.30
Purchase #6	$128.89	12.406%	$144.8801	$144.88	$144.90	$144.90
Purchase #7	$90.77	8.768%	$98.7287	$98.73	$98.75	$98.70
7 purchase totals =	$870.49		$952.9215	$952.92	$952.95	$953.00