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	$130.56	13.219%	$147.8187	$147.82	$147.80	$147.80
Purchase #2	$163.52	9.753%	$179.4681	$179.47	$179.45	$179.50
Purchase #3	$243.94	10.739%	$270.1367	$270.14	$270.15	$270.10
Purchase #4	$78.77	10.237%	$86.8337	$86.83	$86.85	$86.80
Purchase #5	$154.91	8.188%	$167.594	$167.59	$167.60	$167.60
Purchase #6	$121.62	4.579%	$127.189	$127.19	$127.20	$127.20
Purchase #7	$235.57	13.111%	$266.4556	$266.46	$266.45	$266.50
7 purchase totals =	$1,128.89		$1,245.4958	$1,245.50	$1,245.50	$1,245.50