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	$57.82	11.535%	$64.4895	$64.49	$64.50	$64.50
Purchase #2	$7.62	10.547%	$8.4237	$8.42	$8.40	$8.40
Purchase #3	$132.83	9.367%	$145.2722	$145.27	$145.25	$145.30
Purchase #4	$98.28	11.633%	$109.7129	$109.71	$109.70	$109.70
Purchase #5	$6.85	13.537%	$7.7773	$7.78	$7.80	$7.80
Purchase #6	$46.76	4.638%	$48.9287	$48.93	$48.95	$48.90
Purchase #7	$156.34	9.621%	$171.3815	$171.38	$171.40	$171.40
7 purchase totals =	$506.50		$555.9858	$555.98	$556.00	$556.00