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	$194.27	10.354%	$214.3847	$214.38	$214.40	$214.40
Purchase #2	$37.37	6.724%	$39.8828	$39.88	$39.90	$39.90
Purchase #3	$163.61	13.310%	$185.3865	$185.39	$185.40	$185.40
Purchase #4	$177.90	11.603%	$198.5417	$198.54	$198.55	$198.50
Purchase #5	$52.71	9.825%	$57.8888	$57.89	$57.90	$57.90
Purchase #6	$55.27	11.484%	$61.6172	$61.62	$61.60	$61.60
Purchase #7	$38.78	9.183%	$42.3412	$42.34	$42.35	$42.30
7 purchase totals =	$719.91		$800.0429	$800.04	$800.10	$800.00