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	$59.29	12.537%	$66.7232	$66.72	$66.70	$66.70
Purchase #2	$232.86	12.205%	$261.2806	$261.28	$261.30	$261.30
Purchase #3	$172.88	9.586%	$189.4523	$189.45	$189.45	$189.50
Purchase #4	$88.77	6.225%	$94.2959	$94.30	$94.30	$94.30
Purchase #5	$86.80	11.645%	$96.9079	$96.91	$96.90	$96.90
Purchase #6	$69.33	4.737%	$72.6142	$72.61	$72.60	$72.60
Purchase #7	$154.67	7.161%	$165.7459	$165.75	$165.75	$165.70
7 purchase totals =	$864.60		$947.0200	$947.02	$947.00	$947.00