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	$114.55	12.403%	$128.7576	$128.76	$128.75	$128.80
Purchase #2	$27.74	7.621%	$29.8541	$29.85	$29.85	$29.90
Purchase #3	$34.77	6.359%	$36.981	$36.98	$37.00	$37.00
Purchase #4	$25.85	8.656%	$28.0876	$28.09	$28.10	$28.10
Purchase #5	$37.38	3.821%	$38.8083	$38.81	$38.80	$38.80
Purchase #6	$244.47	13.142%	$276.5982	$276.60	$276.60	$276.60
Purchase #7	$185.93	5.552%	$196.2528	$196.25	$196.25	$196.30
7 purchase totals =	$670.69		$735.3396	$735.34	$735.35	$735.50