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	$153.61	11.429%	$171.1661	$171.17	$171.15	$171.20
Purchase #2	$39.45	3.453%	$40.8122	$40.81	$40.80	$40.80
Purchase #3	$120.93	10.854%	$134.0557	$134.06	$134.05	$134.10
Purchase #4	$37.88	6.583%	$40.3736	$40.37	$40.35	$40.40
Purchase #5	$57.52	10.767%	$63.7132	$63.71	$63.70	$63.70
Purchase #6	$47.98	7.272%	$51.4691	$51.47	$51.45	$51.50
Purchase #7	$79.90	8.343%	$86.5661	$86.57	$86.55	$86.60
7 purchase totals =	$537.27		$588.1560	$588.16	$588.05	$588.30