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	$231.61	6.516%	$246.7017	$246.70	$246.70	$246.70
Purchase #2	$131.72	5.870%	$139.452	$139.45	$139.45	$139.50
Purchase #3	$131.88	8.248%	$142.7575	$142.76	$142.75	$142.80
Purchase #4	$38.95	4.795%	$40.8177	$40.82	$40.80	$40.80
Purchase #5	$150.65	5.517%	$158.9614	$158.96	$158.95	$159.00
Purchase #6	$18.81	12.424%	$21.147	$21.15	$21.15	$21.10
Purchase #7	$45.43	4.653%	$47.5439	$47.54	$47.55	$47.50
7 purchase totals =	$749.05		$797.3812	$797.38	$797.35	$797.40