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	$143.93	8.661%	$156.3958	$156.40	$156.40	$156.40
Purchase #2	$199.31	11.447%	$222.125	$222.13	$222.15	$222.10
Purchase #3	$10.77	13.407%	$12.2139	$12.21	$12.20	$12.20
Purchase #4	$82.94	11.200%	$92.2293	$92.23	$92.25	$92.20
Purchase #5	$105.59	6.707%	$112.6719	$112.67	$112.65	$112.70
Purchase #6	$231.28	10.361%	$255.2429	$255.24	$255.25	$255.20
Purchase #7	$72.79	10.583%	$80.4934	$80.49	$80.50	$80.50
7 purchase totals =	$846.61		$931.3722	$931.37	$931.40	$931.30