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	$159.83	3.839%	$165.9659	$165.97	$165.95	$166.00
Purchase #2	$151.46	7.389%	$162.6514	$162.65	$162.65	$162.70
Purchase #3	$241.62	12.380%	$271.5326	$271.53	$271.55	$271.50
Purchase #4	$156.49	6.366%	$166.4522	$166.45	$166.45	$166.50
Purchase #5	$69.53	9.630%	$76.2257	$76.23	$76.25	$76.20
Purchase #6	$106.38	7.494%	$114.3521	$114.35	$114.35	$114.40
Purchase #7	$59.70	4.385%	$62.3178	$62.32	$62.30	$62.30
7 purchase totals =	$945.01		$1,019.4977	$1,019.50	$1,019.50	$1,019.60