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	$213.66	9.242%	$233.4065	$233.41	$233.40	$233.40
Purchase #2	$112.79	9.129%	$123.0866	$123.09	$123.10	$123.10
Purchase #3	$225.59	3.308%	$233.0525	$233.05	$233.05	$233.10
Purchase #4	$20.34	9.253%	$22.2221	$22.22	$22.20	$22.20
Purchase #5	$31.77	13.452%	$36.0437	$36.04	$36.05	$36.00
Purchase #6	$57.34	4.715%	$60.0436	$60.04	$60.05	$60.00
Purchase #7	$80.54	12.773%	$90.8274	$90.83	$90.85	$90.80
7 purchase totals =	$742.03		$798.6824	$798.68	$798.70	$798.60