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	$231.64	12.268%	$260.0576	$260.06	$260.05	$260.10
Purchase #2	$89.88	7.856%	$96.941	$96.94	$96.95	$96.90
Purchase #3	$213.50	4.789%	$223.7245	$223.72	$223.70	$223.70
Purchase #4	$45.26	6.114%	$48.0272	$48.03	$48.05	$48.00
Purchase #5	$185.65	12.818%	$209.4466	$209.45	$209.45	$209.40
Purchase #6	$81.78	10.119%	$90.0553	$90.06	$90.05	$90.10
Purchase #7	$129.38	12.161%	$145.1139	$145.11	$145.10	$145.10
7 purchase totals =	$977.09		$1,073.3661	$1,073.37	$1,073.35	$1,073.30