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	$71.94	9.133%	$78.5103	$78.51	$78.50	$78.50
Purchase #2	$207.80	4.517%	$217.1863	$217.19	$217.20	$217.20
Purchase #3	$17.44	8.806%	$18.9758	$18.98	$19.00	$19.00
Purchase #4	$235.56	8.562%	$255.7286	$255.73	$255.75	$255.70
Purchase #5	$180.88	5.513%	$190.8519	$190.85	$190.85	$190.90
Purchase #6	$228.25	8.813%	$248.3657	$248.37	$248.35	$248.40
Purchase #7	$26.85	10.826%	$29.7568	$29.76	$29.75	$29.80
7 purchase totals =	$968.72		$1,039.3754	$1,039.39	$1,039.40	$1,039.50