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	$80.37	11.301%	$89.4526	$89.45	$89.45	$89.50
Purchase #2	$159.91	5.443%	$168.6139	$168.61	$168.60	$168.60
Purchase #3	$38.71	11.530%	$43.1733	$43.17	$43.15	$43.20
Purchase #4	$159.30	9.844%	$174.9815	$174.98	$175.00	$175.00
Purchase #5	$157.73	6.260%	$167.6039	$167.60	$167.60	$167.60
Purchase #6	$191.38	4.563%	$200.1127	$200.11	$200.10	$200.10
Purchase #7	$80.38	11.391%	$89.5361	$89.54	$89.55	$89.50
7 purchase totals =	$867.78		$933.4740	$933.46	$933.45	$933.50