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	$59.35	11.600%	$66.2346	$66.23	$66.25	$66.20
Purchase #2	$237.59	12.813%	$268.0324	$268.03	$268.05	$268.00
Purchase #3	$198.74	6.864%	$212.3815	$212.38	$212.40	$212.40
Purchase #4	$132.25	5.206%	$139.1349	$139.13	$139.15	$139.10
Purchase #5	$133.28	4.443%	$139.2016	$139.20	$139.20	$139.20
Purchase #6	$154.78	9.110%	$168.8805	$168.88	$168.90	$168.90
Purchase #7	$162.95	9.632%	$178.6453	$178.65	$178.65	$178.60
7 purchase totals =	$1,078.94		$1,172.5108	$1,172.50	$1,172.60	$1,172.40