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	$235.60	12.123%	$264.1618	$264.16	$264.15	$264.20
Purchase #2	$124.94	3.158%	$128.8856	$128.89	$128.90	$128.90
Purchase #3	$95.83	4.868%	$100.495	$100.50	$100.50	$100.50
Purchase #4	$202.33	13.811%	$230.2738	$230.27	$230.25	$230.30
Purchase #5	$212.32	8.567%	$230.5095	$230.51	$230.50	$230.50
Purchase #6	$206.69	4.209%	$215.3896	$215.39	$215.40	$215.40
Purchase #7	$52.83	8.586%	$57.366	$57.37	$57.35	$57.40
7 purchase totals =	$1,130.54		$1,227.0813	$1,227.09	$1,227.05	$1,227.20