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	$164.27	12.640%	$185.0337	$185.03	$185.05	$185.00
Purchase #2	$231.92	9.462%	$253.8643	$253.86	$253.85	$253.90
Purchase #3	$95.42	11.621%	$106.5088	$106.51	$106.50	$106.50
Purchase #4	$54.61	9.448%	$59.7696	$59.77	$59.75	$59.80
Purchase #5	$243.98	13.110%	$275.9658	$275.97	$275.95	$276.00
Purchase #6	$234.95	13.501%	$266.6706	$266.67	$266.65	$266.70
Purchase #7	$249.89	12.138%	$280.2216	$280.22	$280.20	$280.20
7 purchase totals =	$1,275.04		$1,428.0344	$1,428.03	$1,427.95	$1,428.10