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	$91.42	13.326%	$103.6026	$103.60	$103.60	$103.60
Purchase #2	$151.45	6.323%	$161.0262	$161.03	$161.05	$161.00
Purchase #3	$42.95	10.582%	$47.495	$47.50	$47.50	$47.50
Purchase #4	$123.33	6.137%	$130.8988	$130.90	$130.90	$130.90
Purchase #5	$43.76	3.715%	$45.3857	$45.39	$45.40	$45.40
Purchase #6	$29.38	6.824%	$31.3849	$31.38	$31.40	$31.40
Purchase #7	$65.59	13.442%	$74.4066	$74.41	$74.40	$74.40
7 purchase totals =	$547.88		$594.1998	$594.21	$594.25	$594.20