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	$39.75	4.776%	$41.6485	$41.65	$41.65	$41.60
Purchase #2	$35.80	5.576%	$37.7962	$37.80	$37.80	$37.80
Purchase #3	$43.99	7.784%	$47.4142	$47.41	$47.40	$47.40
Purchase #4	$39.45	9.225%	$43.0893	$43.09	$43.10	$43.10
Purchase #5	$34.75	3.272%	$35.887	$35.89	$35.90	$35.90
Purchase #6	$139.39	4.162%	$145.1914	$145.19	$145.20	$145.20
Purchase #7	$177.59	7.484%	$190.8808	$190.88	$190.90	$190.90
7 purchase totals =	$510.72		$541.9074	$541.91	$541.95	$541.90