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	$170.47	3.113%	$175.7767	$175.78	$175.80	$175.80
Purchase #2	$139.89	9.715%	$153.4803	$153.48	$153.50	$153.50
Purchase #3	$107.27	4.400%	$111.9899	$111.99	$112.00	$112.00
Purchase #4	$130.69	5.768%	$138.2282	$138.23	$138.25	$138.20
Purchase #5	$132.26	7.337%	$141.9639	$141.96	$141.95	$142.00
Purchase #6	$141.67	3.522%	$146.6596	$146.66	$146.65	$146.70
Purchase #7	$52.79	12.336%	$59.3022	$59.30	$59.30	$59.30
7 purchase totals =	$875.04		$927.4008	$927.40	$927.45	$927.50