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	$119.30	10.838%	$132.2297	$132.23	$132.25	$132.20
Purchase #2	$170.71	11.264%	$189.9388	$189.94	$189.95	$189.90
Purchase #3	$53.76	9.706%	$58.9779	$58.98	$59.00	$59.00
Purchase #4	$187.44	11.786%	$209.5317	$209.53	$209.55	$209.50
Purchase #5	$144.41	6.536%	$153.8486	$153.85	$153.85	$153.80
Purchase #6	$35.90	13.586%	$40.7774	$40.78	$40.80	$40.80
Purchase #7	$104.64	7.224%	$112.1992	$112.20	$112.20	$112.20
7 purchase totals =	$816.16		$897.5033	$897.51	$897.60	$897.40