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	$248.95	9.510%	$272.6251	$272.63	$272.65	$272.60
Purchase #2	$132.96	7.389%	$142.7844	$142.78	$142.80	$142.80
Purchase #3	$200.55	11.253%	$223.1179	$223.12	$223.10	$223.10
Purchase #4	$36.38	3.164%	$37.5311	$37.53	$37.55	$37.50
Purchase #5	$163.48	6.820%	$174.6293	$174.63	$174.65	$174.60
Purchase #6	$228.83	10.394%	$252.6146	$252.61	$252.60	$252.60
Purchase #7	$152.80	10.336%	$168.5934	$168.59	$168.60	$168.60
7 purchase totals =	$1,163.95		$1,271.8958	$1,271.89	$1,271.95	$1,271.80