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	$74.51	5.191%	$78.3778	$78.38	$78.40	$78.40
Purchase #2	$51.71	13.162%	$58.5161	$58.52	$58.50	$58.50
Purchase #3	$29.42	5.787%	$31.1225	$31.12	$31.10	$31.10
Purchase #4	$47.57	4.245%	$49.5893	$49.59	$49.60	$49.60
Purchase #5	$248.72	3.818%	$258.2161	$258.22	$258.20	$258.20
Purchase #6	$62.32	13.327%	$70.6254	$70.63	$70.65	$70.60
Purchase #7	$220.99	5.851%	$233.9201	$233.92	$233.90	$233.90
7 purchase totals =	$735.24		$780.3673	$780.38	$780.35	$780.30