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	$142.87	12.573%	$160.833	$160.83	$160.85	$160.80
Purchase #2	$148.31	11.119%	$164.8006	$164.80	$164.80	$164.80
Purchase #3	$80.79	3.229%	$83.3987	$83.40	$83.40	$83.40
Purchase #4	$136.62	6.774%	$145.8746	$145.87	$145.85	$145.90
Purchase #5	$57.26	3.542%	$59.2881	$59.29	$59.30	$59.30
Purchase #6	$164.27	7.196%	$176.0909	$176.09	$176.10	$176.10
Purchase #7	$47.98	5.776%	$50.7513	$50.75	$50.75	$50.80
7 purchase totals =	$778.10		$841.0372	$841.03	$841.05	$841.10