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	$32.37	8.480%	$35.115	$35.12	$35.10	$35.10
Purchase #2	$121.68	12.846%	$137.311	$137.31	$137.30	$137.30
Purchase #3	$101.77	6.705%	$108.5937	$108.59	$108.60	$108.60
Purchase #4	$81.74	10.221%	$90.0946	$90.09	$90.10	$90.10
Purchase #5	$102.59	8.475%	$111.2845	$111.28	$111.30	$111.30
Purchase #6	$159.86	6.857%	$170.8216	$170.82	$170.80	$170.80
Purchase #7	$100.25	11.768%	$112.0474	$112.05	$112.05	$112.00
7 purchase totals =	$700.26		$765.2678	$765.26	$765.25	$765.20