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	$175.62	3.381%	$181.5577	$181.56	$181.55	$181.60
Purchase #2	$122.85	13.221%	$139.092	$139.09	$139.10	$139.10
Purchase #3	$98.29	10.614%	$108.7225	$108.72	$108.70	$108.70
Purchase #4	$57.39	4.118%	$59.7533	$59.75	$59.75	$59.80
Purchase #5	$98.39	4.248%	$102.5696	$102.57	$102.55	$102.60
Purchase #6	$120.28	13.382%	$136.3759	$136.38	$136.40	$136.40
Purchase #7	$47.46	9.599%	$52.0157	$52.02	$52.00	$52.00
7 purchase totals =	$720.28		$780.0867	$780.09	$780.05	$780.20