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	$178.40	7.524%	$191.8228	$191.82	$191.80	$191.80
Purchase #2	$167.53	3.197%	$172.8859	$172.89	$172.90	$172.90
Purchase #3	$6.75	6.574%	$7.1937	$7.19	$7.20	$7.20
Purchase #4	$118.25	12.258%	$132.7451	$132.75	$132.75	$132.70
Purchase #5	$21.85	9.302%	$23.8825	$23.88	$23.90	$23.90
Purchase #6	$171.40	6.863%	$183.1632	$183.16	$183.15	$183.20
Purchase #7	$81.27	9.580%	$89.0557	$89.06	$89.05	$89.10
7 purchase totals =	$745.45		$800.7489	$800.75	$800.75	$800.80