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	$112.82	6.582%	$120.2458	$120.25	$120.25	$120.20
Purchase #2	$122.50	8.136%	$132.4666	$132.47	$132.45	$132.50
Purchase #3	$62.34	7.550%	$67.0467	$67.05	$67.05	$67.00
Purchase #4	$38.28	6.723%	$40.8536	$40.85	$40.85	$40.90
Purchase #5	$76.93	11.287%	$85.6131	$85.61	$85.60	$85.60
Purchase #6	$191.90	10.207%	$211.4872	$211.49	$211.50	$211.50
Purchase #7	$137.47	13.152%	$155.5501	$155.55	$155.55	$155.60
7 purchase totals =	$742.24		$813.2631	$813.27	$813.25	$813.30