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	$129.40	12.682%	$145.8105	$145.81	$145.80	$145.80
Purchase #2	$246.87	3.626%	$255.8215	$255.82	$255.80	$255.80
Purchase #3	$138.82	7.575%	$149.3356	$149.34	$149.35	$149.30
Purchase #4	$52.54	4.141%	$54.7157	$54.72	$54.70	$54.70
Purchase #5	$125.38	5.231%	$131.9386	$131.94	$131.95	$131.90
Purchase #6	$48.85	11.666%	$54.5488	$54.55	$54.55	$54.50
Purchase #7	$66.33	9.610%	$72.7043	$72.70	$72.70	$72.70
7 purchase totals =	$808.19		$864.8750	$864.88	$864.85	$864.70