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	$54.39	9.738%	$59.6865	$59.69	$59.70	$59.70
Purchase #2	$125.67	9.540%	$137.6589	$137.66	$137.65	$137.70
Purchase #3	$211.47	4.506%	$220.9988	$221.00	$221.00	$221.00
Purchase #4	$216.32	11.837%	$241.9258	$241.93	$241.95	$241.90
Purchase #5	$94.78	11.765%	$105.9309	$105.93	$105.95	$105.90
Purchase #6	$193.32	6.756%	$206.3807	$206.38	$206.40	$206.40
Purchase #7	$15.47	11.618%	$17.2673	$17.27	$17.25	$17.30
7 purchase totals =	$911.42		$989.8489	$989.86	$989.90	$989.90