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	$132.77	4.152%	$138.2826	$138.28	$138.30	$138.30
Purchase #2	$74.97	10.849%	$83.1035	$83.10	$83.10	$83.10
Purchase #3	$145.36	8.742%	$158.0674	$158.07	$158.05	$158.10
Purchase #4	$42.81	9.611%	$46.9245	$46.92	$46.90	$46.90
Purchase #5	$79.25	11.702%	$88.5238	$88.52	$88.50	$88.50
Purchase #6	$155.89	9.619%	$170.8851	$170.89	$170.90	$170.90
Purchase #7	$166.27	3.213%	$171.6123	$171.61	$171.60	$171.60
7 purchase totals =	$797.32		$857.3992	$857.39	$857.35	$857.40