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	$160.75	4.817%	$168.4933	$168.49	$168.50	$168.50
Purchase #2	$211.80	13.528%	$240.4523	$240.45	$240.45	$240.50
Purchase #3	$72.91	3.549%	$75.4976	$75.50	$75.50	$75.50
Purchase #4	$128.34	9.556%	$140.6042	$140.60	$140.60	$140.60
Purchase #5	$24.54	6.312%	$26.089	$26.09	$26.10	$26.10
Purchase #6	$53.72	10.837%	$59.5416	$59.54	$59.55	$59.50
Purchase #7	$117.56	11.684%	$131.2957	$131.30	$131.30	$131.30
7 purchase totals =	$769.62		$841.9737	$841.97	$842.00	$842.00