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	$79.76	4.712%	$83.5183	$83.52	$83.50	$83.50
Purchase #2	$123.72	12.725%	$139.4634	$139.46	$139.45	$139.50
Purchase #3	$89.97	6.516%	$95.8324	$95.83	$95.85	$95.80
Purchase #4	$237.31	10.218%	$261.5583	$261.56	$261.55	$261.60
Purchase #5	$85.47	5.172%	$89.8905	$89.89	$89.90	$89.90
Purchase #6	$167.58	6.569%	$178.5883	$178.59	$178.60	$178.60
Purchase #7	$24.83	11.365%	$27.6519	$27.65	$27.65	$27.70
7 purchase totals =	$808.64		$876.5031	$876.50	$876.50	$876.60