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	$226.88	12.688%	$255.6665	$255.67	$255.65	$255.70
Purchase #2	$47.82	11.501%	$53.3198	$53.32	$53.30	$53.30
Purchase #3	$109.39	9.227%	$119.4834	$119.48	$119.50	$119.50
Purchase #4	$75.95	3.554%	$78.6493	$78.65	$78.65	$78.60
Purchase #5	$86.73	5.505%	$91.5045	$91.50	$91.50	$91.50
Purchase #6	$209.70	7.328%	$225.0668	$225.07	$225.05	$225.10
Purchase #7	$30.27	5.538%	$31.9464	$31.95	$31.95	$31.90
7 purchase totals =	$786.74		$855.6367	$855.64	$855.60	$855.60