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	$50.45	7.603%	$54.2857	$54.29	$54.30	$54.30
Purchase #2	$61.57	12.793%	$69.4467	$69.45	$69.45	$69.40
Purchase #3	$144.70	13.395%	$164.0826	$164.08	$164.10	$164.10
Purchase #4	$134.78	6.391%	$143.3938	$143.39	$143.40	$143.40
Purchase #5	$244.48	7.731%	$263.3807	$263.38	$263.40	$263.40
Purchase #6	$53.91	9.524%	$59.0444	$59.04	$59.05	$59.00
Purchase #7	$210.32	4.545%	$219.879	$219.88	$219.90	$219.90
7 purchase totals =	$900.21		$973.5129	$973.51	$973.60	$973.50