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	$40.90	4.847%	$42.8824	$42.88	$42.90	$42.90
Purchase #2	$48.50	5.426%	$51.1316	$51.13	$51.15	$51.10
Purchase #3	$37.52	6.562%	$39.9821	$39.98	$40.00	$40.00
Purchase #4	$171.42	10.653%	$189.6814	$189.68	$189.70	$189.70
Purchase #5	$94.64	7.216%	$101.4692	$101.47	$101.45	$101.50
Purchase #6	$62.86	8.439%	$68.1648	$68.16	$68.15	$68.20
Purchase #7	$90.27	9.333%	$98.6949	$98.69	$98.70	$98.70
7 purchase totals =	$546.11		$592.0064	$591.99	$592.05	$592.10