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	$137.85	5.337%	$145.2071	$145.21	$145.20	$145.20
Purchase #2	$192.90	9.260%	$210.7625	$210.76	$210.75	$210.80
Purchase #3	$154.53	11.559%	$172.3921	$172.39	$172.40	$172.40
Purchase #4	$16.50	4.633%	$17.2644	$17.26	$17.25	$17.30
Purchase #5	$112.57	5.810%	$119.1103	$119.11	$119.10	$119.10
Purchase #6	$148.67	13.234%	$168.345	$168.35	$168.35	$168.30
Purchase #7	$250.69	10.262%	$276.4158	$276.42	$276.40	$276.40
7 purchase totals =	$1,013.71		$1,109.4972	$1,109.50	$1,109.45	$1,109.50