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	$81.28	11.451%	$90.5874	$90.59	$90.60	$90.60
Purchase #2	$37.72	8.439%	$40.9032	$40.90	$40.90	$40.90
Purchase #3	$69.93	5.646%	$73.8782	$73.88	$73.90	$73.90
Purchase #4	$21.32	11.842%	$23.8447	$23.84	$23.85	$23.80
Purchase #5	$32.87	13.259%	$37.2282	$37.23	$37.25	$37.20
Purchase #6	$176.46	11.300%	$196.4	$196.40	$196.40	$196.40
Purchase #7	$61.79	12.343%	$69.4167	$69.42	$69.40	$69.40
7 purchase totals =	$481.37		$532.2584	$532.26	$532.30	$532.20