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	$48.44	5.185%	$50.9516	$50.95	$50.95	$51.00
Purchase #2	$50.41	9.548%	$55.2231	$55.22	$55.20	$55.20
Purchase #3	$87.90	9.242%	$96.0237	$96.02	$96.00	$96.00
Purchase #4	$203.71	6.746%	$217.4523	$217.45	$217.45	$217.50
Purchase #5	$52.78	13.256%	$59.7765	$59.78	$59.80	$59.80
Purchase #6	$189.39	10.320%	$208.935	$208.94	$208.95	$208.90
Purchase #7	$132.55	9.208%	$144.7552	$144.76	$144.75	$144.80
7 purchase totals =	$765.18		$833.1174	$833.12	$833.10	$833.20