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	$20.94	12.293%	$23.5142	$23.51	$23.50	$23.50
Purchase #2	$15.57	4.858%	$16.3264	$16.33	$16.35	$16.30
Purchase #3	$72.88	13.194%	$82.4958	$82.50	$82.50	$82.50
Purchase #4	$105.83	7.281%	$113.5355	$113.54	$113.55	$113.50
Purchase #5	$95.27	4.618%	$99.6696	$99.67	$99.65	$99.70
Purchase #6	$10.44	9.138%	$11.394	$11.39	$11.40	$11.40
Purchase #7	$175.43	13.403%	$198.9429	$198.94	$198.95	$198.90
7 purchase totals =	$496.36		$545.8784	$545.88	$545.90	$545.80