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	$221.56	6.724%	$236.4577	$236.46	$236.45	$236.50
Purchase #2	$34.76	6.511%	$37.0232	$37.02	$37.00	$37.00
Purchase #3	$30.78	9.521%	$33.7106	$33.71	$33.70	$33.70
Purchase #4	$222.52	12.730%	$250.8468	$250.85	$250.85	$250.80
Purchase #5	$135.32	5.141%	$142.2768	$142.28	$142.30	$142.30
Purchase #6	$14.64	5.836%	$15.4944	$15.49	$15.50	$15.50
Purchase #7	$210.85	9.627%	$231.1485	$231.15	$231.15	$231.10
7 purchase totals =	$870.43		$946.9580	$946.96	$946.95	$946.90