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	$40.32	5.226%	$42.4271	$42.43	$42.45	$42.40
Purchase #2	$73.44	9.109%	$80.1296	$80.13	$80.15	$80.10
Purchase #3	$9.91	13.551%	$11.2529	$11.25	$11.25	$11.30
Purchase #4	$71.83	9.109%	$78.373	$78.37	$78.35	$78.40
Purchase #5	$92.52	9.813%	$101.599	$101.60	$101.60	$101.60
Purchase #6	$63.87	6.262%	$67.8695	$67.87	$67.85	$67.90
Purchase #7	$116.25	10.553%	$128.5179	$128.52	$128.50	$128.50
7 purchase totals =	$468.14		$510.1690	$510.17	$510.15	$510.20