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	$99.89	3.508%	$103.3941	$103.39	$103.40	$103.40
Purchase #2	$117.65	4.305%	$122.7148	$122.71	$122.70	$122.70
Purchase #3	$200.91	10.268%	$221.5394	$221.54	$221.55	$221.50
Purchase #4	$85.38	6.112%	$90.5984	$90.60	$90.60	$90.60
Purchase #5	$31.38	3.259%	$32.4027	$32.40	$32.40	$32.40
Purchase #6	$114.82	6.770%	$122.5933	$122.59	$122.60	$122.60
Purchase #7	$216.53	8.298%	$234.4977	$234.50	$234.50	$234.50
7 purchase totals =	$866.56		$927.7404	$927.73	$927.75	$927.70