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	$236.50	5.411%	$249.297	$249.30	$249.30	$249.30
Purchase #2	$178.58	9.671%	$195.8505	$195.85	$195.85	$195.90
Purchase #3	$152.39	8.432%	$165.2395	$165.24	$165.25	$165.20
Purchase #4	$32.58	6.181%	$34.5938	$34.59	$34.60	$34.60
Purchase #5	$137.68	12.455%	$154.828	$154.83	$154.85	$154.80
Purchase #6	$123.61	7.468%	$132.8412	$132.84	$132.85	$132.80
Purchase #7	$140.89	5.320%	$148.3853	$148.39	$148.40	$148.40
7 purchase totals =	$1,002.23		$1,081.0353	$1,081.04	$1,081.10	$1,081.00