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	$49.73	7.565%	$53.4921	$53.49	$53.50	$53.50
Purchase #2	$221.45	9.202%	$241.8278	$241.83	$241.85	$241.80
Purchase #3	$115.74	10.115%	$127.4471	$127.45	$127.45	$127.40
Purchase #4	$127.97	11.185%	$142.2834	$142.28	$142.30	$142.30
Purchase #5	$78.50	3.373%	$81.1478	$81.15	$81.15	$81.10
Purchase #6	$66.29	9.185%	$72.3787	$72.38	$72.40	$72.40
Purchase #7	$46.62	3.737%	$48.3622	$48.36	$48.35	$48.40
7 purchase totals =	$706.30		$766.9391	$766.94	$767.00	$766.90