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	$80.63	10.846%	$89.3751	$89.38	$89.40	$89.40
Purchase #2	$216.51	13.259%	$245.2171	$245.22	$245.20	$245.20
Purchase #3	$146.82	5.111%	$154.324	$154.32	$154.30	$154.30
Purchase #4	$228.85	10.210%	$252.2156	$252.22	$252.20	$252.20
Purchase #5	$187.62	12.150%	$210.4158	$210.42	$210.40	$210.40
Purchase #6	$57.64	6.641%	$61.4679	$61.47	$61.45	$61.50
Purchase #7	$99.50	12.736%	$112.1723	$112.17	$112.15	$112.20
7 purchase totals =	$1,017.57		$1,125.1878	$1,125.20	$1,125.10	$1,125.20