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	$10.25	11.112%	$11.389	$11.39	$11.40	$11.40
Purchase #2	$242.78	7.480%	$260.9399	$260.94	$260.95	$260.90
Purchase #3	$63.99	5.449%	$67.4768	$67.48	$67.50	$67.50
Purchase #4	$217.59	3.812%	$225.8845	$225.88	$225.90	$225.90
Purchase #5	$93.29	13.229%	$105.6313	$105.63	$105.65	$105.60
Purchase #6	$12.40	8.651%	$13.4727	$13.47	$13.45	$13.50
Purchase #7	$172.45	3.261%	$178.0736	$178.07	$178.05	$178.10
7 purchase totals =	$812.75		$862.8678	$862.86	$862.90	$862.90