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	$107.88	6.190%	$114.5578	$114.56	$114.55	$114.60
Purchase #2	$232.55	3.605%	$240.9334	$240.93	$240.95	$240.90
Purchase #3	$161.83	13.373%	$183.4715	$183.47	$183.45	$183.50
Purchase #4	$116.51	13.327%	$132.0373	$132.04	$132.05	$132.00
Purchase #5	$177.38	7.320%	$190.3642	$190.36	$190.35	$190.40
Purchase #6	$166.47	11.609%	$185.7955	$185.80	$185.80	$185.80
Purchase #7	$229.89	13.833%	$261.6907	$261.69	$261.70	$261.70
7 purchase totals =	$1,192.51		$1,308.8504	$1,308.85	$1,308.85	$1,308.90