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	$10.76	5.837%	$11.3881	$11.39	$11.40	$11.40
Purchase #2	$33.42	12.229%	$37.5069	$37.51	$37.50	$37.50
Purchase #3	$227.94	9.415%	$249.4006	$249.40	$249.40	$249.40
Purchase #4	$159.29	3.440%	$164.7696	$164.77	$164.75	$164.80
Purchase #5	$35.31	13.313%	$40.0108	$40.01	$40.00	$40.00
Purchase #6	$60.68	13.530%	$68.89	$68.89	$68.90	$68.90
Purchase #7	$35.86	8.133%	$38.7765	$38.78	$38.80	$38.80
7 purchase totals =	$563.26		$610.7425	$610.75	$610.75	$610.80