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	$12.89	5.529%	$13.6027	$13.60	$13.60	$13.60
Purchase #2	$39.98	9.438%	$43.7533	$43.75	$43.75	$43.80
Purchase #3	$153.28	13.172%	$173.47	$173.47	$173.45	$173.50
Purchase #4	$78.42	3.603%	$81.2455	$81.25	$81.25	$81.20
Purchase #5	$39.31	10.657%	$43.4993	$43.50	$43.50	$43.50
Purchase #6	$96.90	12.116%	$108.6404	$108.64	$108.65	$108.60
Purchase #7	$149.56	8.582%	$162.3952	$162.40	$162.40	$162.40
7 purchase totals =	$570.34		$626.6064	$626.61	$626.60	$626.60