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	$136.34	12.369%	$153.2039	$153.20	$153.20	$153.20
Purchase #2	$54.75	12.861%	$61.7914	$61.79	$61.80	$61.80
Purchase #3	$37.96	5.593%	$40.0831	$40.08	$40.10	$40.10
Purchase #4	$151.65	6.400%	$161.3556	$161.36	$161.35	$161.40
Purchase #5	$158.98	3.602%	$164.7065	$164.71	$164.70	$164.70
Purchase #6	$214.66	4.211%	$223.6993	$223.70	$223.70	$223.70
Purchase #7	$116.41	6.165%	$123.5867	$123.59	$123.60	$123.60
7 purchase totals =	$870.75		$928.4265	$928.43	$928.45	$928.50