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	$26.73	7.489%	$28.7318	$28.73	$28.75	$28.70
Purchase #2	$72.90	9.197%	$79.6046	$79.60	$79.60	$79.60
Purchase #3	$247.78	7.541%	$266.4651	$266.47	$266.45	$266.50
Purchase #4	$194.38	3.288%	$200.7712	$200.77	$200.75	$200.80
Purchase #5	$163.66	5.293%	$172.3225	$172.32	$172.30	$172.30
Purchase #6	$42.63	4.163%	$44.4047	$44.40	$44.40	$44.40
Purchase #7	$117.93	7.835%	$127.1698	$127.17	$127.15	$127.20
7 purchase totals =	$866.01		$919.4697	$919.46	$919.40	$919.50