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	$183.63	12.294%	$206.2055	$206.21	$206.20	$206.20
Purchase #2	$115.70	6.856%	$123.6324	$123.63	$123.65	$123.60
Purchase #3	$228.37	5.689%	$241.362	$241.36	$241.35	$241.40
Purchase #4	$116.30	10.811%	$128.8732	$128.87	$128.85	$128.90
Purchase #5	$35.72	10.109%	$39.3309	$39.33	$39.35	$39.30
Purchase #6	$149.85	10.504%	$165.5902	$165.59	$165.60	$165.60
Purchase #7	$158.93	3.497%	$164.4878	$164.49	$164.50	$164.50
7 purchase totals =	$988.50		$1,069.4820	$1,069.48	$1,069.50	$1,069.50