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	$111.63	10.302%	$123.1301	$123.13	$123.15	$123.10
Purchase #2	$77.59	4.121%	$80.7875	$80.79	$80.80	$80.80
Purchase #3	$185.35	11.337%	$206.3631	$206.36	$206.35	$206.40
Purchase #4	$126.55	12.133%	$141.9043	$141.90	$141.90	$141.90
Purchase #5	$239.84	6.493%	$255.4128	$255.41	$255.40	$255.40
Purchase #6	$78.36	6.306%	$83.3014	$83.30	$83.30	$83.30
Purchase #7	$11.91	4.569%	$12.4542	$12.45	$12.45	$12.50
7 purchase totals =	$831.23		$903.3534	$903.34	$903.35	$903.40