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	$57.48	13.312%	$65.1317	$65.13	$65.15	$65.10
Purchase #2	$196.45	4.484%	$205.2588	$205.26	$205.25	$205.30
Purchase #3	$204.78	5.718%	$216.4893	$216.49	$216.50	$216.50
Purchase #4	$48.47	12.353%	$54.4575	$54.46	$54.45	$54.50
Purchase #5	$125.78	8.471%	$136.4348	$136.43	$136.45	$136.40
Purchase #6	$129.54	6.515%	$137.9795	$137.98	$138.00	$138.00
Purchase #7	$26.56	4.347%	$27.7146	$27.71	$27.70	$27.70
7 purchase totals =	$789.06		$843.4662	$843.46	$843.50	$843.50