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	$39.73	7.606%	$42.7519	$42.75	$42.75	$42.80
Purchase #2	$160.67	12.330%	$180.4806	$180.48	$180.50	$180.50
Purchase #3	$172.47	10.177%	$190.0223	$190.02	$190.00	$190.00
Purchase #4	$85.28	7.229%	$91.4449	$91.44	$91.45	$91.40
Purchase #5	$164.80	5.505%	$173.8722	$173.87	$173.85	$173.90
Purchase #6	$43.38	13.795%	$49.3643	$49.36	$49.35	$49.40
Purchase #7	$29.42	3.274%	$30.3832	$30.38	$30.40	$30.40
7 purchase totals =	$695.75		$758.3194	$758.30	$758.30	$758.40