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	$10.91	10.592%	$12.0656	$12.07	$12.05	$12.10
Purchase #2	$246.61	12.158%	$276.5928	$276.59	$276.60	$276.60
Purchase #3	$210.28	13.757%	$239.2082	$239.21	$239.20	$239.20
Purchase #4	$163.84	5.230%	$172.4088	$172.41	$172.40	$172.40
Purchase #5	$26.42	5.500%	$27.8731	$27.87	$27.85	$27.90
Purchase #6	$70.25	10.400%	$77.556	$77.56	$77.55	$77.60
Purchase #7	$189.38	3.695%	$196.3776	$196.38	$196.40	$196.40
7 purchase totals =	$917.69		$1,002.0821	$1,002.09	$1,002.05	$1,002.20