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	$105.57	12.260%	$118.5129	$118.51	$118.50	$118.50
Purchase #2	$54.34	4.632%	$56.857	$56.86	$56.85	$56.90
Purchase #3	$157.37	9.353%	$172.0888	$172.09	$172.10	$172.10
Purchase #4	$181.31	6.353%	$192.8286	$192.83	$192.85	$192.80
Purchase #5	$43.28	10.656%	$47.8919	$47.89	$47.90	$47.90
Purchase #6	$155.40	7.199%	$166.5872	$166.59	$166.60	$166.60
Purchase #7	$102.80	7.857%	$110.877	$110.88	$110.90	$110.90
7 purchase totals =	$800.07		$865.6434	$865.65	$865.70	$865.70