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	$183.83	3.496%	$190.2567	$190.26	$190.25	$190.30
Purchase #2	$50.74	8.870%	$55.2406	$55.24	$55.25	$55.20
Purchase #3	$220.52	13.161%	$249.5426	$249.54	$249.55	$249.50
Purchase #4	$39.46	8.658%	$42.8764	$42.88	$42.90	$42.90
Purchase #5	$54.83	4.210%	$57.1383	$57.14	$57.15	$57.10
Purchase #6	$163.39	9.412%	$178.7683	$178.77	$178.75	$178.80
Purchase #7	$132.26	5.763%	$139.8821	$139.88	$139.90	$139.90
7 purchase totals =	$845.03		$913.7050	$913.71	$913.75	$913.70