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	$6.32	4.678%	$6.6156	$6.62	$6.60	$6.60
Purchase #2	$151.85	13.531%	$172.3968	$172.40	$172.40	$172.40
Purchase #3	$223.93	9.801%	$245.8774	$245.88	$245.90	$245.90
Purchase #4	$205.68	8.286%	$222.7226	$222.72	$222.70	$222.70
Purchase #5	$180.51	6.199%	$191.6998	$191.70	$191.70	$191.70
Purchase #6	$200.46	7.677%	$215.8493	$215.85	$215.85	$215.80
Purchase #7	$233.40	11.318%	$259.8162	$259.82	$259.80	$259.80
7 purchase totals =	$1,202.15		$1,314.9777	$1,314.99	$1,314.95	$1,314.90