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	$230.98	13.371%	$261.8643	$261.86	$261.85	$261.90
Purchase #2	$42.94	11.383%	$47.8279	$47.83	$47.85	$47.80
Purchase #3	$240.87	9.691%	$264.2127	$264.21	$264.20	$264.20
Purchase #4	$49.54	10.753%	$54.867	$54.87	$54.85	$54.90
Purchase #5	$161.74	3.785%	$167.8619	$167.86	$167.85	$167.90
Purchase #6	$116.50	7.111%	$124.7843	$124.78	$124.80	$124.80
Purchase #7	$43.38	10.865%	$48.0932	$48.09	$48.10	$48.10
7 purchase totals =	$885.95		$969.5113	$969.50	$969.50	$969.60