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	$89.46	12.754%	$100.8697	$100.87	$100.85	$100.90
Purchase #2	$91.37	3.113%	$94.2143	$94.21	$94.20	$94.20
Purchase #3	$79.84	4.114%	$83.1246	$83.12	$83.10	$83.10
Purchase #4	$24.77	10.837%	$27.4543	$27.45	$27.45	$27.50
Purchase #5	$38.57	6.219%	$40.9687	$40.97	$40.95	$41.00
Purchase #6	$65.59	10.803%	$72.6757	$72.68	$72.70	$72.70
Purchase #7	$235.85	10.780%	$261.2746	$261.27	$261.25	$261.30
7 purchase totals =	$625.45		$680.5819	$680.57	$680.50	$680.70