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	$111.62	4.683%	$116.8472	$116.85	$116.85	$116.80
Purchase #2	$98.56	7.408%	$105.8613	$105.86	$105.85	$105.90
Purchase #3	$123.56	12.656%	$139.1978	$139.20	$139.20	$139.20
Purchase #4	$78.96	12.391%	$88.7439	$88.74	$88.75	$88.70
Purchase #5	$132.73	4.454%	$138.6418	$138.64	$138.65	$138.60
Purchase #6	$45.60	8.296%	$49.383	$49.38	$49.40	$49.40
Purchase #7	$34.36	10.225%	$37.8733	$37.87	$37.85	$37.90
7 purchase totals =	$625.39		$676.5483	$676.54	$676.55	$676.50