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	$168.86	9.484%	$184.8747	$184.87	$184.85	$184.90
Purchase #2	$120.77	9.676%	$132.4557	$132.46	$132.45	$132.50
Purchase #3	$49.47	12.794%	$55.7992	$55.80	$55.80	$55.80
Purchase #4	$77.57	9.654%	$85.0586	$85.06	$85.05	$85.10
Purchase #5	$134.68	9.766%	$147.8328	$147.83	$147.85	$147.80
Purchase #6	$104.61	7.213%	$112.1555	$112.16	$112.15	$112.20
Purchase #7	$122.77	7.156%	$131.5554	$131.56	$131.55	$131.60
7 purchase totals =	$778.73		$849.7319	$849.74	$849.70	$849.90