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	$57.26	4.117%	$59.6174	$59.62	$59.60	$59.60
Purchase #2	$24.77	12.874%	$27.9589	$27.96	$27.95	$28.00
Purchase #3	$165.82	4.244%	$172.8574	$172.86	$172.85	$172.90
Purchase #4	$181.29	5.166%	$190.6554	$190.66	$190.65	$190.70
Purchase #5	$93.29	13.425%	$105.8142	$105.81	$105.80	$105.80
Purchase #6	$212.42	3.694%	$220.2668	$220.27	$220.25	$220.30
Purchase #7	$104.93	8.124%	$113.4545	$113.45	$113.45	$113.50
7 purchase totals =	$839.78		$890.6246	$890.63	$890.55	$890.80