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	$143.69	12.464%	$161.5995	$161.60	$161.60	$161.60
Purchase #2	$128.74	13.693%	$146.3684	$146.37	$146.35	$146.40
Purchase #3	$179.36	4.731%	$187.8455	$187.85	$187.85	$187.80
Purchase #4	$77.92	10.133%	$85.8156	$85.82	$85.80	$85.80
Purchase #5	$209.95	5.633%	$221.7765	$221.78	$221.80	$221.80
Purchase #6	$39.78	9.577%	$43.5897	$43.59	$43.60	$43.60
Purchase #7	$144.60	6.694%	$154.2795	$154.28	$154.30	$154.30
7 purchase totals =	$924.04		$1,001.2747	$1,001.29	$1,001.30	$1,001.30