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	$27.77	3.130%	$28.6392	$28.64	$28.65	$28.60
Purchase #2	$180.86	10.586%	$200.0058	$200.01	$200.00	$200.00
Purchase #3	$88.54	12.295%	$99.426	$99.43	$99.45	$99.40
Purchase #4	$87.80	3.103%	$90.5244	$90.52	$90.50	$90.50
Purchase #5	$80.47	4.174%	$83.8288	$83.83	$83.85	$83.80
Purchase #6	$118.37	7.607%	$127.3744	$127.37	$127.35	$127.40
Purchase #7	$113.83	5.456%	$120.0406	$120.04	$120.05	$120.00
7 purchase totals =	$697.64		$749.8392	$749.84	$749.85	$749.70