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	$25.46	8.251%	$27.5607	$27.56	$27.55	$27.60
Purchase #2	$48.37	11.478%	$53.9219	$53.92	$53.90	$53.90
Purchase #3	$118.38	11.620%	$132.1358	$132.14	$132.15	$132.10
Purchase #4	$144.28	3.185%	$148.8753	$148.88	$148.90	$148.90
Purchase #5	$49.77	3.461%	$51.4925	$51.49	$51.50	$51.50
Purchase #6	$181.52	13.554%	$206.1232	$206.12	$206.10	$206.10
Purchase #7	$164.98	12.362%	$185.3748	$185.37	$185.35	$185.40
7 purchase totals =	$732.76		$805.4842	$805.48	$805.45	$805.50