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	$58.34	10.543%	$64.4908	$64.49	$64.50	$64.50
Purchase #2	$158.78	4.188%	$165.4297	$165.43	$165.45	$165.40
Purchase #3	$109.50	12.824%	$123.5423	$123.54	$123.55	$123.50
Purchase #4	$74.96	7.432%	$80.531	$80.53	$80.55	$80.50
Purchase #5	$65.59	5.283%	$69.0551	$69.06	$69.05	$69.10
Purchase #6	$27.86	6.397%	$29.6422	$29.64	$29.65	$29.60
Purchase #7	$179.94	9.282%	$196.642	$196.64	$196.65	$196.60
7 purchase totals =	$674.97		$729.3331	$729.33	$729.40	$729.20