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	$49.81	9.425%	$54.5046	$54.50	$54.50	$54.50
Purchase #2	$32.47	11.384%	$36.1664	$36.17	$36.15	$36.20
Purchase #3	$167.68	3.523%	$173.5874	$173.59	$173.60	$173.60
Purchase #4	$115.49	6.851%	$123.4022	$123.40	$123.40	$123.40
Purchase #5	$85.69	5.767%	$90.6317	$90.63	$90.65	$90.60
Purchase #6	$63.55	11.385%	$70.7852	$70.79	$70.80	$70.80
Purchase #7	$96.51	4.728%	$101.073	$101.07	$101.05	$101.10
7 purchase totals =	$611.20		$650.1505	$650.15	$650.15	$650.20