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	$120.60	9.311%	$131.8291	$131.83	$131.85	$131.80
Purchase #2	$151.58	5.173%	$159.4212	$159.42	$159.40	$159.40
Purchase #3	$46.30	9.194%	$50.5568	$50.56	$50.55	$50.60
Purchase #4	$136.34	11.127%	$151.5106	$151.51	$151.50	$151.50
Purchase #5	$35.67	13.416%	$40.4555	$40.46	$40.45	$40.50
Purchase #6	$101.89	3.283%	$105.235	$105.24	$105.25	$105.20
Purchase #7	$128.42	9.419%	$140.5159	$140.52	$140.50	$140.50
7 purchase totals =	$720.80		$779.5241	$779.54	$779.50	$779.50