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	$169.45	6.208%	$179.9695	$179.97	$179.95	$180.00
Purchase #2	$245.90	13.644%	$279.4506	$279.45	$279.45	$279.50
Purchase #3	$112.60	6.798%	$120.2545	$120.25	$120.25	$120.30
Purchase #4	$85.34	5.313%	$89.8741	$89.87	$89.85	$89.90
Purchase #5	$193.50	5.541%	$204.2218	$204.22	$204.20	$204.20
Purchase #6	$29.86	12.183%	$33.4978	$33.50	$33.50	$33.50
Purchase #7	$141.68	4.729%	$148.38	$148.38	$148.40	$148.40
7 purchase totals =	$978.33		$1,055.6483	$1,055.64	$1,055.60	$1,055.80