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	$123.90	12.226%	$139.048	$139.05	$139.05	$139.00
Purchase #2	$65.58	6.178%	$69.6315	$69.63	$69.65	$69.60
Purchase #3	$88.58	11.662%	$98.9102	$98.91	$98.90	$98.90
Purchase #4	$156.91	9.307%	$171.5136	$171.51	$171.50	$171.50
Purchase #5	$24.85	4.629%	$26.0003	$26.00	$26.00	$26.00
Purchase #6	$93.61	12.249%	$105.0763	$105.08	$105.10	$105.10
Purchase #7	$97.34	3.153%	$100.4091	$100.41	$100.40	$100.40
7 purchase totals =	$650.77		$710.5890	$710.59	$710.60	$710.50