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	$87.79	12.790%	$99.0183	$99.02	$99.00	$99.00
Purchase #2	$107.35	8.535%	$116.5123	$116.51	$116.50	$116.50
Purchase #3	$99.64	3.557%	$103.1842	$103.18	$103.20	$103.20
Purchase #4	$105.35	10.718%	$116.6414	$116.64	$116.65	$116.60
Purchase #5	$102.29	10.250%	$112.7747	$112.77	$112.75	$112.80
Purchase #6	$28.41	11.865%	$31.7808	$31.78	$31.80	$31.80
Purchase #7	$52.40	11.671%	$58.5156	$58.52	$58.50	$58.50
7 purchase totals =	$583.23		$638.4273	$638.42	$638.40	$638.40