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	$72.77	11.131%	$80.87	$80.87	$80.85	$80.90
Purchase #2	$216.26	9.314%	$236.4025	$236.40	$236.40	$236.40
Purchase #3	$181.91	7.778%	$196.059	$196.06	$196.05	$196.10
Purchase #4	$21.48	6.377%	$22.8498	$22.85	$22.85	$22.80
Purchase #5	$204.25	9.254%	$223.1513	$223.15	$223.15	$223.20
Purchase #6	$171.91	10.558%	$190.0603	$190.06	$190.05	$190.10
Purchase #7	$10.71	3.504%	$11.0853	$11.09	$11.10	$11.10
7 purchase totals =	$879.29		$960.4782	$960.48	$960.45	$960.60