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	$121.72	5.133%	$127.9679	$127.97	$127.95	$128.00
Purchase #2	$44.31	11.305%	$49.3192	$49.32	$49.30	$49.30
Purchase #3	$153.41	12.688%	$172.8747	$172.87	$172.85	$172.90
Purchase #4	$171.38	3.639%	$177.6165	$177.62	$177.60	$177.60
Purchase #5	$69.46	4.799%	$72.7934	$72.79	$72.80	$72.80
Purchase #6	$80.66	3.176%	$83.2218	$83.22	$83.20	$83.20
Purchase #7	$83.88	4.286%	$87.4751	$87.48	$87.50	$87.50
7 purchase totals =	$724.82		$771.2686	$771.27	$771.20	$771.30