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	$24.35	10.431%	$26.8899	$26.89	$26.90	$26.90
Purchase #2	$153.69	11.801%	$171.827	$171.83	$171.85	$171.80
Purchase #3	$94.45	8.643%	$102.6133	$102.61	$102.60	$102.60
Purchase #4	$61.47	7.568%	$66.122	$66.12	$66.10	$66.10
Purchase #5	$242.74	4.479%	$253.6123	$253.61	$253.60	$253.60
Purchase #6	$182.50	12.403%	$205.1355	$205.14	$205.15	$205.10
Purchase #7	$168.61	13.742%	$191.7804	$191.78	$191.80	$191.80
7 purchase totals =	$927.81		$1,017.9804	$1,017.98	$1,018.00	$1,017.90