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	$29.87	10.489%	$33.0031	$33.00	$33.00	$33.00
Purchase #2	$43.96	13.602%	$49.9394	$49.94	$49.95	$49.90
Purchase #3	$246.44	6.237%	$261.8105	$261.81	$261.80	$261.80
Purchase #4	$54.44	4.519%	$56.9001	$56.90	$56.90	$56.90
Purchase #5	$113.46	12.201%	$127.3033	$127.30	$127.30	$127.30
Purchase #6	$157.94	13.718%	$179.6062	$179.61	$179.60	$179.60
Purchase #7	$105.79	8.104%	$114.3632	$114.36	$114.35	$114.40
7 purchase totals =	$751.90		$822.9258	$822.92	$822.90	$822.90