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	$156.46	7.722%	$168.5418	$168.54	$168.55	$168.50
Purchase #2	$123.45	6.634%	$131.6397	$131.64	$131.65	$131.60
Purchase #3	$53.72	6.488%	$57.2054	$57.21	$57.20	$57.20
Purchase #4	$167.94	3.409%	$173.6651	$173.67	$173.65	$173.70
Purchase #5	$66.62	5.574%	$70.3334	$70.33	$70.35	$70.30
Purchase #6	$52.40	7.677%	$56.4227	$56.42	$56.40	$56.40
Purchase #7	$172.81	5.341%	$182.0398	$182.04	$182.05	$182.00
7 purchase totals =	$793.40		$839.8479	$839.85	$839.85	$839.70