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	$198.34	5.206%	$208.6656	$208.67	$208.65	$208.70
Purchase #2	$164.81	11.259%	$183.366	$183.37	$183.35	$183.40
Purchase #3	$75.52	8.502%	$81.9407	$81.94	$81.95	$81.90
Purchase #4	$11.87	8.677%	$12.9	$12.90	$12.90	$12.90
Purchase #5	$125.36	13.175%	$141.8762	$141.88	$141.90	$141.90
Purchase #6	$66.79	8.239%	$72.2928	$72.29	$72.30	$72.30
Purchase #7	$42.56	6.657%	$45.3932	$45.39	$45.40	$45.40
7 purchase totals =	$685.25		$746.4345	$746.44	$746.45	$746.50