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	$81.39	12.333%	$91.4278	$91.43	$91.45	$91.40
Purchase #2	$121.60	5.549%	$128.3476	$128.35	$128.35	$128.30
Purchase #3	$86.26	4.164%	$89.8519	$89.85	$89.85	$89.90
Purchase #4	$20.45	6.118%	$21.7011	$21.70	$21.70	$21.70
Purchase #5	$201.59	13.111%	$228.0205	$228.02	$228.00	$228.00
Purchase #6	$157.68	12.111%	$176.7766	$176.78	$176.80	$176.80
Purchase #7	$50.85	10.473%	$56.1755	$56.18	$56.20	$56.20
7 purchase totals =	$719.82		$792.3010	$792.31	$792.35	$792.30