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	$144.88	5.771%	$153.241	$153.24	$153.25	$153.20
Purchase #2	$144.44	9.579%	$158.2759	$158.28	$158.30	$158.30
Purchase #3	$152.64	6.445%	$162.4776	$162.48	$162.50	$162.50
Purchase #4	$13.89	8.108%	$15.0162	$15.02	$15.00	$15.00
Purchase #5	$41.55	10.384%	$45.8646	$45.86	$45.85	$45.90
Purchase #6	$188.94	13.682%	$214.7908	$214.79	$214.80	$214.80
Purchase #7	$80.85	3.217%	$83.4509	$83.45	$83.45	$83.50
7 purchase totals =	$767.19		$833.1170	$833.12	$833.15	$833.20