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	$18.91	3.610%	$19.5927	$19.59	$19.60	$19.60
Purchase #2	$140.55	11.218%	$156.3169	$156.32	$156.30	$156.30
Purchase #3	$137.80	8.455%	$149.451	$149.45	$149.45	$149.50
Purchase #4	$208.38	12.247%	$233.9003	$233.90	$233.90	$233.90
Purchase #5	$91.31	8.119%	$98.7235	$98.72	$98.70	$98.70
Purchase #6	$92.37	8.726%	$100.4302	$100.43	$100.45	$100.40
Purchase #7	$171.45	7.841%	$184.8934	$184.89	$184.90	$184.90
7 purchase totals =	$860.77		$943.3080	$943.30	$943.30	$943.30