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	$144.88	13.321%	$164.1795	$164.18	$164.20	$164.20
Purchase #2	$153.72	11.570%	$171.5054	$171.51	$171.50	$171.50
Purchase #3	$113.25	10.231%	$124.8366	$124.84	$124.85	$124.80
Purchase #4	$5.51	11.572%	$6.1476	$6.15	$6.15	$6.10
Purchase #5	$220.25	8.381%	$238.7092	$238.71	$238.70	$238.70
Purchase #6	$151.57	9.527%	$166.0101	$166.01	$166.00	$166.00
Purchase #7	$96.28	5.384%	$101.4637	$101.46	$101.45	$101.50
7 purchase totals =	$885.46		$972.8521	$972.86	$972.85	$972.80