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	$51.85	10.807%	$57.4534	$57.45	$57.45	$57.50
Purchase #2	$119.56	12.816%	$134.8828	$134.88	$134.90	$134.90
Purchase #3	$57.63	6.369%	$61.3005	$61.30	$61.30	$61.30
Purchase #4	$243.78	5.200%	$256.4566	$256.46	$256.45	$256.50
Purchase #5	$66.68	5.123%	$70.096	$70.10	$70.10	$70.10
Purchase #6	$118.80	3.133%	$122.522	$122.52	$122.50	$122.50
Purchase #7	$132.74	8.711%	$144.303	$144.30	$144.30	$144.30
7 purchase totals =	$791.04		$847.0143	$847.01	$847.00	$847.10