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	$141.86	5.597%	$149.7999	$149.80	$149.80	$149.80
Purchase #2	$190.51	6.617%	$203.116	$203.12	$203.10	$203.10
Purchase #3	$37.75	12.845%	$42.599	$42.60	$42.60	$42.60
Purchase #4	$33.81	11.454%	$37.6826	$37.68	$37.70	$37.70
Purchase #5	$9.84	12.686%	$11.0883	$11.09	$11.10	$11.10
Purchase #6	$67.63	6.512%	$72.0341	$72.03	$72.05	$72.00
Purchase #7	$134.52	11.691%	$150.2467	$150.25	$150.25	$150.20
7 purchase totals =	$615.92		$666.5666	$666.57	$666.60	$666.50