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	$76.67	3.687%	$79.4968	$79.50	$79.50	$79.50
Purchase #2	$121.48	10.104%	$133.7543	$133.75	$133.75	$133.80
Purchase #3	$239.68	11.715%	$267.7585	$267.76	$267.75	$267.80
Purchase #4	$204.28	10.573%	$225.8785	$225.88	$225.90	$225.90
Purchase #5	$74.78	4.808%	$78.3754	$78.38	$78.40	$78.40
Purchase #6	$62.27	7.587%	$66.9944	$66.99	$67.00	$67.00
Purchase #7	$222.89	11.401%	$248.3017	$248.30	$248.30	$248.30
7 purchase totals =	$1,002.05		$1,100.5596	$1,100.56	$1,100.60	$1,100.70