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	$100.56	4.559%	$105.1445	$105.14	$105.15	$105.10
Purchase #2	$21.28	12.714%	$23.9855	$23.99	$24.00	$24.00
Purchase #3	$173.82	12.816%	$196.0968	$196.10	$196.10	$196.10
Purchase #4	$227.87	11.274%	$253.5601	$253.56	$253.55	$253.60
Purchase #5	$20.72	6.835%	$22.1362	$22.14	$22.15	$22.10
Purchase #6	$18.60	11.472%	$20.7338	$20.73	$20.75	$20.70
Purchase #7	$63.97	4.768%	$67.0201	$67.02	$67.00	$67.00
7 purchase totals =	$626.82		$688.6770	$688.68	$688.70	$688.60