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	$151.47	9.810%	$166.3292	$166.33	$166.35	$166.30
Purchase #2	$158.29	5.390%	$166.8218	$166.82	$166.80	$166.80
Purchase #3	$32.25	6.377%	$34.3066	$34.31	$34.30	$34.30
Purchase #4	$94.63	5.498%	$99.8328	$99.83	$99.85	$99.80
Purchase #5	$200.90	10.452%	$221.8981	$221.90	$221.90	$221.90
Purchase #6	$221.32	3.393%	$228.8294	$228.83	$228.85	$228.80
Purchase #7	$39.84	12.579%	$44.8515	$44.85	$44.85	$44.90
7 purchase totals =	$898.70		$962.8694	$962.87	$962.90	$962.80