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	$99.58	3.782%	$103.3461	$103.35	$103.35	$103.30
Purchase #2	$133.59	4.513%	$139.6189	$139.62	$139.60	$139.60
Purchase #3	$81.28	10.531%	$89.8396	$89.84	$89.85	$89.80
Purchase #4	$43.92	12.383%	$49.3586	$49.36	$49.35	$49.40
Purchase #5	$131.70	13.657%	$149.6863	$149.69	$149.70	$149.70
Purchase #6	$112.25	13.386%	$127.2758	$127.28	$127.30	$127.30
Purchase #7	$188.32	10.159%	$207.4514	$207.45	$207.45	$207.50
7 purchase totals =	$790.64		$866.5767	$866.59	$866.60	$866.60