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	$31.78	7.463%	$34.1517	$34.15	$34.15	$34.20
Purchase #2	$219.96	7.854%	$237.2357	$237.24	$237.25	$237.20
Purchase #3	$100.94	4.420%	$105.4015	$105.40	$105.40	$105.40
Purchase #4	$223.86	4.314%	$233.5173	$233.52	$233.50	$233.50
Purchase #5	$39.53	7.204%	$42.3777	$42.38	$42.40	$42.40
Purchase #6	$41.33	5.637%	$43.6598	$43.66	$43.65	$43.70
Purchase #7	$99.82	12.103%	$111.9012	$111.90	$111.90	$111.90
7 purchase totals =	$757.22		$808.2449	$808.25	$808.25	$808.30