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	$142.45	7.865%	$153.6537	$153.65	$153.65	$153.70
Purchase #2	$34.52	9.402%	$37.7656	$37.77	$37.75	$37.80
Purchase #3	$132.31	9.622%	$145.0409	$145.04	$145.05	$145.00
Purchase #4	$132.25	6.168%	$140.4072	$140.41	$140.40	$140.40
Purchase #5	$51.49	9.839%	$56.5561	$56.56	$56.55	$56.60
Purchase #6	$173.71	9.127%	$189.5645	$189.56	$189.55	$189.60
Purchase #7	$249.78	10.321%	$275.5598	$275.56	$275.55	$275.60
7 purchase totals =	$916.51		$998.5478	$998.55	$998.50	$998.70