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	$218.89	13.389%	$248.1972	$248.20	$248.20	$248.20
Purchase #2	$233.61	8.160%	$252.6726	$252.67	$252.65	$252.70
Purchase #3	$203.30	9.828%	$223.2803	$223.28	$223.30	$223.30
Purchase #4	$223.60	8.533%	$242.6798	$242.68	$242.70	$242.70
Purchase #5	$61.74	9.128%	$67.3756	$67.38	$67.40	$67.40
Purchase #6	$176.78	11.357%	$196.8569	$196.86	$196.85	$196.90
Purchase #7	$18.41	10.407%	$20.3259	$20.33	$20.35	$20.30
7 purchase totals =	$1,136.33		$1,251.3883	$1,251.40	$1,251.45	$1,251.50