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	$210.29	5.846%	$222.5836	$222.58	$222.60	$222.60
Purchase #2	$27.74	3.400%	$28.6832	$28.68	$28.70	$28.70
Purchase #3	$54.68	9.493%	$59.8708	$59.87	$59.85	$59.90
Purchase #4	$51.86	12.178%	$58.1755	$58.18	$58.20	$58.20
Purchase #5	$139.63	11.646%	$155.8913	$155.89	$155.90	$155.90
Purchase #6	$99.74	11.420%	$111.1303	$111.13	$111.15	$111.10
Purchase #7	$201.44	9.245%	$220.0631	$220.06	$220.05	$220.10
7 purchase totals =	$785.38		$856.3978	$856.39	$856.45	$856.50