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	$158.84	6.210%	$168.704	$168.70	$168.70	$168.70
Purchase #2	$240.83	7.743%	$259.4775	$259.48	$259.50	$259.50
Purchase #3	$70.55	9.162%	$77.0138	$77.01	$77.00	$77.00
Purchase #4	$87.84	12.447%	$98.7734	$98.77	$98.75	$98.80
Purchase #5	$155.52	6.130%	$165.0534	$165.05	$165.05	$165.10
Purchase #6	$81.41	10.322%	$89.8131	$89.81	$89.80	$89.80
Purchase #7	$72.38	4.854%	$75.8933	$75.89	$75.90	$75.90
7 purchase totals =	$867.37		$934.7285	$934.71	$934.70	$934.80