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	$170.27	7.775%	$183.5085	$183.51	$183.50	$183.50
Purchase #2	$86.71	3.507%	$89.7509	$89.75	$89.75	$89.80
Purchase #3	$218.30	9.162%	$238.3006	$238.30	$238.30	$238.30
Purchase #4	$84.25	13.570%	$95.6827	$95.68	$95.70	$95.70
Purchase #5	$18.80	8.260%	$20.3529	$20.35	$20.35	$20.40
Purchase #6	$226.36	5.509%	$238.8302	$238.83	$238.85	$238.80
Purchase #7	$166.94	10.178%	$183.9312	$183.93	$183.95	$183.90
7 purchase totals =	$971.63		$1,050.3570	$1,050.35	$1,050.40	$1,050.40