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	$59.41	11.625%	$66.3164	$66.32	$66.30	$66.30
Purchase #2	$122.45	7.450%	$131.5725	$131.57	$131.55	$131.60
Purchase #3	$63.99	12.511%	$71.9958	$72.00	$72.00	$72.00
Purchase #4	$114.40	11.661%	$127.7402	$127.74	$127.75	$127.70
Purchase #5	$59.43	8.666%	$64.5802	$64.58	$64.60	$64.60
Purchase #6	$99.77	7.403%	$107.156	$107.16	$107.15	$107.20
Purchase #7	$21.45	5.548%	$22.64	$22.64	$22.65	$22.60
7 purchase totals =	$540.90		$592.0011	$592.01	$592.00	$592.00