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	$89.82	12.725%	$101.2496	$101.25	$101.25	$101.20
Purchase #2	$207.77	12.440%	$233.6166	$233.62	$233.60	$233.60
Purchase #3	$166.77	13.865%	$189.8927	$189.89	$189.90	$189.90
Purchase #4	$92.83	7.651%	$99.9324	$99.93	$99.95	$99.90
Purchase #5	$59.66	6.806%	$63.7205	$63.72	$63.70	$63.70
Purchase #6	$156.68	10.283%	$172.7914	$172.79	$172.80	$172.80
Purchase #7	$109.71	5.749%	$116.0172	$116.02	$116.00	$116.00
7 purchase totals =	$883.24		$977.2204	$977.22	$977.20	$977.10