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	$49.82	10.187%	$54.8952	$54.90	$54.90	$54.90
Purchase #2	$193.33	11.610%	$215.7756	$215.78	$215.80	$215.80
Purchase #3	$28.44	4.470%	$29.7113	$29.71	$29.70	$29.70
Purchase #4	$51.71	5.275%	$54.4377	$54.44	$54.45	$54.40
Purchase #5	$22.83	6.780%	$24.3779	$24.38	$24.40	$24.40
Purchase #6	$19.82	9.583%	$21.7194	$21.72	$21.70	$21.70
Purchase #7	$55.58	3.526%	$57.5398	$57.54	$57.55	$57.50
7 purchase totals =	$421.53		$458.4569	$458.47	$458.50	$458.40