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	$51.89	7.682%	$55.8762	$55.88	$55.90	$55.90
Purchase #2	$158.67	6.395%	$168.8169	$168.82	$168.80	$168.80
Purchase #3	$242.82	12.719%	$273.7043	$273.70	$273.70	$273.70
Purchase #4	$80.75	4.380%	$84.2869	$84.29	$84.30	$84.30
Purchase #5	$52.35	5.854%	$55.4146	$55.41	$55.40	$55.40
Purchase #6	$51.42	9.548%	$56.3296	$56.33	$56.35	$56.30
Purchase #7	$153.95	11.867%	$172.2192	$172.22	$172.20	$172.20
7 purchase totals =	$791.85		$866.6477	$866.65	$866.65	$866.60