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	$31.97	9.572%	$35.0302	$35.03	$35.05	$35.00
Purchase #2	$36.49	10.328%	$40.2587	$40.26	$40.25	$40.30
Purchase #3	$134.77	6.784%	$143.9128	$143.91	$143.90	$143.90
Purchase #4	$39.87	3.477%	$41.2563	$41.26	$41.25	$41.30
Purchase #5	$29.89	5.551%	$31.5492	$31.55	$31.55	$31.50
Purchase #6	$45.71	12.713%	$51.5211	$51.52	$51.50	$51.50
Purchase #7	$10.31	7.550%	$11.0884	$11.09	$11.10	$11.10
7 purchase totals =	$329.01		$354.6167	$354.62	$354.60	$354.60