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	$226.83	12.420%	$255.0023	$255.00	$255.00	$255.00
Purchase #2	$89.39	11.426%	$99.6037	$99.60	$99.60	$99.60
Purchase #3	$65.73	8.443%	$71.2796	$71.28	$71.30	$71.30
Purchase #4	$18.83	10.873%	$20.8774	$20.88	$20.90	$20.90
Purchase #5	$60.84	12.175%	$68.2473	$68.25	$68.25	$68.20
Purchase #6	$164.87	7.162%	$176.678	$176.68	$176.70	$176.70
Purchase #7	$81.89	11.629%	$91.413	$91.41	$91.40	$91.40
7 purchase totals =	$708.38		$783.1013	$783.10	$783.15	$783.10