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	$238.45	7.744%	$256.9156	$256.92	$256.90	$256.90
Purchase #2	$161.69	5.513%	$170.604	$170.60	$170.60	$170.60
Purchase #3	$41.50	11.174%	$46.1372	$46.14	$46.15	$46.10
Purchase #4	$153.80	12.439%	$172.9312	$172.93	$172.95	$172.90
Purchase #5	$249.47	5.792%	$263.9193	$263.92	$263.90	$263.90
Purchase #6	$18.47	13.266%	$20.9202	$20.92	$20.90	$20.90
Purchase #7	$169.65	8.392%	$183.887	$183.89	$183.90	$183.90
7 purchase totals =	$1,033.03		$1,115.3145	$1,115.32	$1,115.30	$1,115.20