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	$229.45	11.826%	$256.5848	$256.58	$256.60	$256.60
Purchase #2	$52.85	4.353%	$55.1506	$55.15	$55.15	$55.20
Purchase #3	$51.75	7.576%	$55.6706	$55.67	$55.65	$55.70
Purchase #4	$161.58	10.713%	$178.8901	$178.89	$178.90	$178.90
Purchase #5	$131.65	11.342%	$146.5817	$146.58	$146.60	$146.60
Purchase #6	$82.56	13.475%	$93.685	$93.69	$93.70	$93.70
Purchase #7	$25.72	11.507%	$28.6796	$28.68	$28.70	$28.70
7 purchase totals =	$735.56		$815.2424	$815.24	$815.30	$815.40