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	$72.93	7.477%	$78.383	$78.38	$78.40	$78.40
Purchase #2	$141.50	9.616%	$155.1066	$155.11	$155.10	$155.10
Purchase #3	$35.91	6.463%	$38.2309	$38.23	$38.25	$38.20
Purchase #4	$164.41	10.593%	$181.826	$181.83	$181.85	$181.80
Purchase #5	$50.65	5.624%	$53.4986	$53.50	$53.50	$53.50
Purchase #6	$48.69	3.685%	$50.4842	$50.48	$50.50	$50.50
Purchase #7	$56.84	11.569%	$63.4158	$63.42	$63.40	$63.40
7 purchase totals =	$570.93		$620.9451	$620.95	$621.00	$620.90