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	$15.92	13.574%	$18.081	$18.08	$18.10	$18.10
Purchase #2	$173.34	13.213%	$196.2434	$196.24	$196.25	$196.20
Purchase #3	$83.49	13.238%	$94.5424	$94.54	$94.55	$94.50
Purchase #4	$128.32	12.508%	$144.3703	$144.37	$144.35	$144.40
Purchase #5	$52.73	13.530%	$59.8644	$59.86	$59.85	$59.90
Purchase #6	$13.59	12.553%	$15.296	$15.30	$15.30	$15.30
Purchase #7	$31.52	5.195%	$33.1575	$33.16	$33.15	$33.20
7 purchase totals =	$498.91		$561.5550	$561.55	$561.55	$561.60