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	$120.61	9.600%	$132.1886	$132.19	$132.20	$132.20
Purchase #2	$102.29	8.454%	$110.9376	$110.94	$110.95	$110.90
Purchase #3	$80.67	12.657%	$90.8804	$90.88	$90.90	$90.90
Purchase #4	$149.85	8.620%	$162.7671	$162.77	$162.75	$162.80
Purchase #5	$39.78	6.308%	$42.2893	$42.29	$42.30	$42.30
Purchase #6	$143.47	3.575%	$148.5991	$148.60	$148.60	$148.60
Purchase #7	$149.95	4.171%	$156.2044	$156.20	$156.20	$156.20
7 purchase totals =	$786.62		$843.8665	$843.87	$843.90	$843.90