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	$76.91	4.278%	$80.2002	$80.20	$80.20	$80.20
Purchase #2	$28.27	7.646%	$30.4315	$30.43	$30.45	$30.40
Purchase #3	$200.46	11.761%	$224.0361	$224.04	$224.05	$224.00
Purchase #4	$38.27	11.292%	$42.5914	$42.59	$42.60	$42.60
Purchase #5	$162.74	8.390%	$176.3939	$176.39	$176.40	$176.40
Purchase #6	$206.58	7.643%	$222.3689	$222.37	$222.35	$222.40
Purchase #7	$222.92	11.493%	$248.5402	$248.54	$248.55	$248.50
7 purchase totals =	$936.15		$1,024.5622	$1,024.56	$1,024.60	$1,024.50