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	$137.47	10.244%	$151.5524	$151.55	$151.55	$151.60
Purchase #2	$160.50	6.689%	$171.2358	$171.24	$171.25	$171.20
Purchase #3	$117.89	3.735%	$122.2932	$122.29	$122.30	$122.30
Purchase #4	$222.32	7.315%	$238.5827	$238.58	$238.60	$238.60
Purchase #5	$25.70	7.387%	$27.5985	$27.60	$27.60	$27.60
Purchase #6	$27.71	12.354%	$31.1333	$31.13	$31.15	$31.10
Purchase #7	$226.53	6.755%	$241.8321	$241.83	$241.85	$241.80
7 purchase totals =	$918.12		$984.2280	$984.22	$984.30	$984.20