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	$64.97	3.873%	$67.4863	$67.49	$67.50	$67.50
Purchase #2	$80.31	13.236%	$90.9398	$90.94	$90.95	$90.90
Purchase #3	$160.85	4.830%	$168.6191	$168.62	$168.60	$168.60
Purchase #4	$52.60	5.609%	$55.5503	$55.55	$55.55	$55.60
Purchase #5	$72.55	7.251%	$77.8106	$77.81	$77.80	$77.80
Purchase #6	$78.58	4.275%	$81.9393	$81.94	$81.95	$81.90
Purchase #7	$202.95	13.337%	$230.0174	$230.02	$230.00	$230.00
7 purchase totals =	$712.81		$772.3628	$772.37	$772.35	$772.30