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	$151.46	5.180%	$159.3056	$159.31	$159.30	$159.30
Purchase #2	$175.45	10.467%	$193.8144	$193.81	$193.80	$193.80
Purchase #3	$117.42	5.354%	$123.7067	$123.71	$123.70	$123.70
Purchase #4	$35.53	11.836%	$39.7353	$39.74	$39.75	$39.70
Purchase #5	$167.34	10.723%	$185.2839	$185.28	$185.30	$185.30
Purchase #6	$161.88	13.752%	$184.1417	$184.14	$184.15	$184.10
Purchase #7	$161.46	6.630%	$172.1648	$172.16	$172.15	$172.20
7 purchase totals =	$970.54		$1,058.1524	$1,058.15	$1,058.15	$1,058.10