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	$170.36	6.157%	$180.8491	$180.85	$180.85	$180.80
Purchase #2	$150.70	11.735%	$168.3846	$168.38	$168.40	$168.40
Purchase #3	$217.76	3.383%	$225.1268	$225.13	$225.15	$225.10
Purchase #4	$97.72	5.434%	$103.0301	$103.03	$103.05	$103.00
Purchase #5	$234.38	10.812%	$259.7212	$259.72	$259.70	$259.70
Purchase #6	$72.50	8.642%	$78.7655	$78.77	$78.75	$78.80
Purchase #7	$57.40	8.662%	$62.372	$62.37	$62.35	$62.40
7 purchase totals =	$1,000.82		$1,078.2493	$1,078.25	$1,078.25	$1,078.20