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	$249.89	10.645%	$276.4908	$276.49	$276.50	$276.50
Purchase #2	$127.77	13.182%	$144.6126	$144.61	$144.60	$144.60
Purchase #3	$124.85	3.111%	$128.7341	$128.73	$128.75	$128.70
Purchase #4	$64.28	11.148%	$71.4459	$71.45	$71.45	$71.40
Purchase #5	$128.32	3.461%	$132.7612	$132.76	$132.75	$132.80
Purchase #6	$188.99	5.299%	$199.0046	$199.00	$199.00	$199.00
Purchase #7	$11.26	4.679%	$11.7869	$11.79	$11.80	$11.80
7 purchase totals =	$895.36		$964.8361	$964.83	$964.85	$964.80