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	$18.55	8.559%	$20.1377	$20.14	$20.15	$20.10
Purchase #2	$95.68	9.860%	$105.114	$105.11	$105.10	$105.10
Purchase #3	$141.83	13.818%	$161.4281	$161.43	$161.45	$161.40
Purchase #4	$156.68	12.768%	$176.6849	$176.68	$176.70	$176.70
Purchase #5	$55.86	5.693%	$59.0401	$59.04	$59.05	$59.00
Purchase #6	$222.81	8.432%	$241.5973	$241.60	$241.60	$241.60
Purchase #7	$57.39	3.405%	$59.3441	$59.34	$59.35	$59.30
7 purchase totals =	$748.80		$823.3462	$823.34	$823.40	$823.20