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	$82.89	6.189%	$88.0201	$88.02	$88.00	$88.00
Purchase #2	$136.25	11.121%	$151.4024	$151.40	$151.40	$151.40
Purchase #3	$200.32	6.665%	$213.6713	$213.67	$213.65	$213.70
Purchase #4	$150.45	9.574%	$164.8541	$164.85	$164.85	$164.90
Purchase #5	$104.92	12.565%	$118.1032	$118.10	$118.10	$118.10
Purchase #6	$80.78	11.690%	$90.2232	$90.22	$90.20	$90.20
Purchase #7	$60.68	8.445%	$65.8044	$65.80	$65.80	$65.80
7 purchase totals =	$816.29		$892.0787	$892.06	$892.00	$892.10