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	$60.60	12.797%	$68.355	$68.36	$68.35	$68.40
Purchase #2	$176.82	5.822%	$187.1145	$187.11	$187.10	$187.10
Purchase #3	$86.39	6.610%	$92.1004	$92.10	$92.10	$92.10
Purchase #4	$27.60	5.617%	$29.1503	$29.15	$29.15	$29.20
Purchase #5	$250.99	11.364%	$279.5125	$279.51	$279.50	$279.50
Purchase #6	$195.57	11.242%	$217.556	$217.56	$217.55	$217.60
Purchase #7	$124.72	3.103%	$128.5901	$128.59	$128.60	$128.60
7 purchase totals =	$922.69		$1,002.3788	$1,002.38	$1,002.35	$1,002.50