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	$182.48	4.293%	$190.3139	$190.31	$190.30	$190.30
Purchase #2	$62.28	8.585%	$67.6267	$67.63	$67.65	$67.60
Purchase #3	$142.30	10.681%	$157.4991	$157.50	$157.50	$157.50
Purchase #4	$157.94	6.831%	$168.7289	$168.73	$168.75	$168.70
Purchase #5	$75.28	3.737%	$78.0932	$78.09	$78.10	$78.10
Purchase #6	$50.37	11.617%	$56.2215	$56.22	$56.20	$56.20
Purchase #7	$245.66	5.105%	$258.2009	$258.20	$258.20	$258.20
7 purchase totals =	$916.31		$976.6842	$976.68	$976.70	$976.60