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	$130.80	6.634%	$139.4773	$139.48	$139.50	$139.50
Purchase #2	$169.39	12.399%	$190.3927	$190.39	$190.40	$190.40
Purchase #3	$237.73	6.598%	$253.4154	$253.42	$253.40	$253.40
Purchase #4	$194.79	13.725%	$221.5249	$221.52	$221.50	$221.50
Purchase #5	$28.67	13.394%	$32.5101	$32.51	$32.50	$32.50
Purchase #6	$128.83	9.859%	$141.5313	$141.53	$141.55	$141.50
Purchase #7	$208.26	4.216%	$217.0402	$217.04	$217.05	$217.00
7 purchase totals =	$1,098.47		$1,195.8919	$1,195.89	$1,195.90	$1,195.80