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	$28.94	9.277%	$31.6248	$31.62	$31.60	$31.60
Purchase #2	$230.26	13.729%	$261.8724	$261.87	$261.85	$261.90
Purchase #3	$17.86	7.214%	$19.1484	$19.15	$19.15	$19.10
Purchase #4	$97.94	6.798%	$104.598	$104.60	$104.60	$104.60
Purchase #5	$92.98	7.607%	$100.053	$100.05	$100.05	$100.10
Purchase #6	$59.76	3.388%	$61.7847	$61.78	$61.80	$61.80
Purchase #7	$21.51	12.829%	$24.2695	$24.27	$24.25	$24.30
7 purchase totals =	$549.25		$603.3508	$603.34	$603.30	$603.40