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	$11.68	5.665%	$12.3417	$12.34	$12.35	$12.30
Purchase #2	$134.40	12.847%	$151.6664	$151.67	$151.65	$151.70
Purchase #3	$29.25	8.427%	$31.7149	$31.71	$31.70	$31.70
Purchase #4	$105.76	6.579%	$112.718	$112.72	$112.70	$112.70
Purchase #5	$238.63	9.650%	$261.6578	$261.66	$261.65	$261.70
Purchase #6	$205.46	7.504%	$220.8777	$220.88	$220.90	$220.90
Purchase #7	$215.91	3.236%	$222.8968	$222.90	$222.90	$222.90
7 purchase totals =	$941.09		$1,013.8733	$1,013.88	$1,013.85	$1,013.90