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	$49.48	10.357%	$54.6046	$54.60	$54.60	$54.60
Purchase #2	$102.83	5.467%	$108.4517	$108.45	$108.45	$108.50
Purchase #3	$67.29	7.733%	$72.4935	$72.49	$72.50	$72.50
Purchase #4	$186.70	5.135%	$196.287	$196.29	$196.30	$196.30
Purchase #5	$98.86	5.237%	$104.0373	$104.04	$104.05	$104.00
Purchase #6	$227.74	13.830%	$259.2364	$259.24	$259.25	$259.20
Purchase #7	$6.54	12.624%	$7.3656	$7.37	$7.35	$7.40
7 purchase totals =	$739.44		$802.4761	$802.48	$802.50	$802.50