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	$187.65	11.692%	$209.59	$209.59	$209.60	$209.60
Purchase #2	$98.94	13.314%	$112.1129	$112.11	$112.10	$112.10
Purchase #3	$207.32	7.483%	$222.8338	$222.83	$222.85	$222.80
Purchase #4	$10.79	6.843%	$11.5284	$11.53	$11.55	$11.50
Purchase #5	$12.59	6.864%	$13.4542	$13.45	$13.45	$13.50
Purchase #6	$194.59	5.557%	$205.4034	$205.40	$205.40	$205.40
Purchase #7	$125.88	4.292%	$131.2828	$131.28	$131.30	$131.30
7 purchase totals =	$837.76		$906.2055	$906.19	$906.25	$906.20