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	$138.79	3.367%	$143.4631	$143.46	$143.45	$143.50
Purchase #2	$54.34	3.692%	$56.3462	$56.35	$56.35	$56.30
Purchase #3	$203.47	11.788%	$227.455	$227.46	$227.45	$227.50
Purchase #4	$79.89	7.327%	$85.7435	$85.74	$85.75	$85.70
Purchase #5	$23.49	4.184%	$24.4728	$24.47	$24.45	$24.50
Purchase #6	$140.72	7.577%	$151.3824	$151.38	$151.40	$151.40
Purchase #7	$89.36	7.527%	$96.0861	$96.09	$96.10	$96.10
7 purchase totals =	$730.06		$784.9491	$784.95	$784.95	$785.00