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	$20.49	11.262%	$22.7976	$22.80	$22.80	$22.80
Purchase #2	$217.78	12.467%	$244.9306	$244.93	$244.95	$244.90
Purchase #3	$6.92	8.319%	$7.4957	$7.50	$7.50	$7.50
Purchase #4	$127.89	13.419%	$145.0516	$145.05	$145.05	$145.10
Purchase #5	$127.63	3.768%	$132.4391	$132.44	$132.45	$132.40
Purchase #6	$112.91	12.867%	$127.4381	$127.44	$127.45	$127.40
Purchase #7	$87.38	10.221%	$96.3111	$96.31	$96.30	$96.30
7 purchase totals =	$701.00		$776.4638	$776.47	$776.50	$776.40