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	$132.48	4.356%	$138.2508	$138.25	$138.25	$138.30
Purchase #2	$97.87	11.725%	$109.3453	$109.35	$109.35	$109.30
Purchase #3	$74.76	8.429%	$81.0615	$81.06	$81.05	$81.10
Purchase #4	$171.81	9.428%	$188.0082	$188.01	$188.00	$188.00
Purchase #5	$214.69	3.435%	$222.0646	$222.06	$222.05	$222.10
Purchase #6	$34.34	8.462%	$37.2459	$37.25	$37.25	$37.20
Purchase #7	$59.38	8.581%	$64.4754	$64.48	$64.50	$64.50
7 purchase totals =	$785.33		$840.4517	$840.46	$840.45	$840.50