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	$206.42	8.510%	$223.9863	$223.99	$224.00	$224.00
Purchase #2	$161.67	4.874%	$169.5498	$169.55	$169.55	$169.50
Purchase #3	$86.62	4.274%	$90.3221	$90.32	$90.30	$90.30
Purchase #4	$19.67	4.547%	$20.5644	$20.56	$20.55	$20.60
Purchase #5	$62.64	13.205%	$70.9116	$70.91	$70.90	$70.90
Purchase #6	$90.70	5.309%	$95.5153	$95.52	$95.50	$95.50
Purchase #7	$146.87	4.459%	$153.4189	$153.42	$153.40	$153.40
7 purchase totals =	$774.59		$824.2684	$824.27	$824.20	$824.20