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	$54.51	5.693%	$57.6133	$57.61	$57.60	$57.60
Purchase #2	$168.62	6.671%	$179.8686	$179.87	$179.85	$179.90
Purchase #3	$191.95	12.204%	$215.3756	$215.38	$215.40	$215.40
Purchase #4	$156.67	11.242%	$174.2828	$174.28	$174.30	$174.30
Purchase #5	$100.46	11.457%	$111.9697	$111.97	$111.95	$112.00
Purchase #6	$108.60	9.601%	$119.0267	$119.03	$119.05	$119.00
Purchase #7	$100.35	12.234%	$112.6268	$112.63	$112.65	$112.60
7 purchase totals =	$881.16		$970.7635	$970.77	$970.80	$970.80