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	$48.61	9.177%	$53.0709	$53.07	$53.05	$53.10
Purchase #2	$151.50	3.225%	$156.3859	$156.39	$156.40	$156.40
Purchase #3	$109.87	12.385%	$123.4774	$123.48	$123.50	$123.50
Purchase #4	$19.74	9.666%	$21.6481	$21.65	$21.65	$21.60
Purchase #5	$90.39	4.350%	$94.322	$94.32	$94.30	$94.30
Purchase #6	$51.46	8.422%	$55.794	$55.79	$55.80	$55.80
Purchase #7	$20.59	10.665%	$22.7859	$22.79	$22.80	$22.80
7 purchase totals =	$492.16		$527.4842	$527.49	$527.50	$527.50