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	$6.92	9.677%	$7.5896	$7.59	$7.60	$7.60
Purchase #2	$52.85	13.862%	$60.1761	$60.18	$60.20	$60.20
Purchase #3	$248.92	9.457%	$272.4604	$272.46	$272.45	$272.50
Purchase #4	$93.67	7.266%	$100.4761	$100.48	$100.50	$100.50
Purchase #5	$233.31	12.207%	$261.7902	$261.79	$261.80	$261.80
Purchase #6	$120.94	5.767%	$127.9146	$127.91	$127.90	$127.90
Purchase #7	$6.27	12.168%	$7.0329	$7.03	$7.05	$7.00
7 purchase totals =	$762.88		$837.4399	$837.44	$837.50	$837.50