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	$245.44	4.180%	$255.6994	$255.70	$255.70	$255.70
Purchase #2	$61.35	9.855%	$67.396	$67.40	$67.40	$67.40
Purchase #3	$73.52	13.271%	$83.2768	$83.28	$83.30	$83.30
Purchase #4	$239.71	13.249%	$271.4692	$271.47	$271.45	$271.50
Purchase #5	$33.46	6.689%	$35.6981	$35.70	$35.70	$35.70
Purchase #6	$76.68	13.239%	$86.8317	$86.83	$86.85	$86.80
Purchase #7	$61.97	6.834%	$66.205	$66.21	$66.20	$66.20
7 purchase totals =	$792.13		$866.5762	$866.59	$866.60	$866.60