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	$125.83	8.541%	$136.5771	$136.58	$136.60	$136.60
Purchase #2	$61.92	7.366%	$66.481	$66.48	$66.50	$66.50
Purchase #3	$64.41	3.437%	$66.6238	$66.62	$66.60	$66.60
Purchase #4	$84.82	8.739%	$92.2324	$92.23	$92.25	$92.20
Purchase #5	$131.93	5.569%	$139.2772	$139.28	$139.30	$139.30
Purchase #6	$81.39	11.763%	$90.9639	$90.96	$90.95	$91.00
Purchase #7	$71.92	12.446%	$80.8712	$80.87	$80.85	$80.90
7 purchase totals =	$622.22		$673.0266	$673.02	$673.05	$673.10