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	$161.87	10.451%	$178.787	$178.79	$178.80	$178.80
Purchase #2	$181.77	13.278%	$205.9054	$205.91	$205.90	$205.90
Purchase #3	$169.66	6.505%	$180.6964	$180.70	$180.70	$180.70
Purchase #4	$175.37	7.139%	$187.8897	$187.89	$187.90	$187.90
Purchase #5	$35.72	7.410%	$38.3669	$38.37	$38.35	$38.40
Purchase #6	$132.82	7.826%	$143.2145	$143.21	$143.20	$143.20
Purchase #7	$39.88	13.174%	$45.1338	$45.13	$45.15	$45.10
7 purchase totals =	$897.09		$979.9937	$980.00	$980.00	$980.00