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	$113.44	13.181%	$128.3925	$128.39	$128.40	$128.40
Purchase #2	$188.45	12.465%	$211.9403	$211.94	$211.95	$211.90
Purchase #3	$171.38	10.246%	$188.9396	$188.94	$188.95	$188.90
Purchase #4	$77.96	5.252%	$82.0545	$82.05	$82.05	$82.10
Purchase #5	$218.82	9.640%	$239.9142	$239.91	$239.90	$239.90
Purchase #6	$78.92	8.455%	$85.5927	$85.59	$85.60	$85.60
Purchase #7	$52.62	8.475%	$57.0795	$57.08	$57.10	$57.10
7 purchase totals =	$901.59		$993.9133	$993.90	$993.95	$993.90