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	$135.45	6.509%	$144.2664	$144.27	$144.25	$144.30
Purchase #2	$73.83	8.429%	$80.0531	$80.05	$80.05	$80.10
Purchase #3	$156.66	9.649%	$171.7761	$171.78	$171.80	$171.80
Purchase #4	$54.96	11.282%	$61.1606	$61.16	$61.15	$61.20
Purchase #5	$227.96	8.548%	$247.446	$247.45	$247.45	$247.40
Purchase #6	$43.48	4.344%	$45.3688	$45.37	$45.35	$45.40
Purchase #7	$138.85	9.583%	$152.156	$152.16	$152.15	$152.20
7 purchase totals =	$831.19		$902.2270	$902.24	$902.20	$902.40