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	$144.96	10.233%	$159.7938	$159.79	$159.80	$159.80
Purchase #2	$232.60	3.751%	$241.3248	$241.32	$241.30	$241.30
Purchase #3	$45.78	11.729%	$51.1495	$51.15	$51.15	$51.10
Purchase #4	$64.30	6.699%	$68.6075	$68.61	$68.60	$68.60
Purchase #5	$126.66	12.156%	$142.0568	$142.06	$142.05	$142.10
Purchase #6	$197.32	12.684%	$222.3481	$222.35	$222.35	$222.30
Purchase #7	$89.69	3.571%	$92.8928	$92.89	$92.90	$92.90
7 purchase totals =	$901.31		$978.1733	$978.17	$978.15	$978.10