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	$150.55	3.871%	$156.3778	$156.38	$156.40	$156.40
Purchase #2	$47.88	10.474%	$52.895	$52.90	$52.90	$52.90
Purchase #3	$17.72	4.612%	$18.5372	$18.54	$18.55	$18.50
Purchase #4	$103.95	4.526%	$108.6548	$108.65	$108.65	$108.70
Purchase #5	$21.67	10.230%	$23.8868	$23.89	$23.90	$23.90
Purchase #6	$147.73	7.123%	$158.2528	$158.25	$158.25	$158.30
Purchase #7	$93.29	8.168%	$100.9099	$100.91	$100.90	$100.90
7 purchase totals =	$582.79		$619.5143	$619.52	$619.55	$619.60