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	$202.77	8.262%	$219.5229	$219.52	$219.50	$219.50
Purchase #2	$124.48	6.229%	$132.2339	$132.23	$132.25	$132.20
Purchase #3	$111.68	10.485%	$123.3896	$123.39	$123.40	$123.40
Purchase #4	$34.77	5.789%	$36.7828	$36.78	$36.80	$36.80
Purchase #5	$142.74	12.649%	$160.7952	$160.80	$160.80	$160.80
Purchase #6	$37.60	6.687%	$40.1143	$40.11	$40.10	$40.10
Purchase #7	$100.36	3.406%	$103.7783	$103.78	$103.80	$103.80
7 purchase totals =	$754.40		$816.6170	$816.61	$816.65	$816.60