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	$18.43	13.259%	$20.8736	$20.87	$20.85	$20.90
Purchase #2	$235.41	9.295%	$257.2914	$257.29	$257.30	$257.30
Purchase #3	$119.94	9.599%	$131.453	$131.45	$131.45	$131.50
Purchase #4	$91.74	8.867%	$99.8746	$99.87	$99.85	$99.90
Purchase #5	$132.40	12.836%	$149.3949	$149.39	$149.40	$149.40
Purchase #6	$31.38	5.470%	$33.0965	$33.10	$33.10	$33.10
Purchase #7	$249.75	4.687%	$261.4558	$261.46	$261.45	$261.50
7 purchase totals =	$879.05		$953.4398	$953.43	$953.40	$953.60