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	$51.81	5.280%	$54.5456	$54.55	$54.55	$54.50
Purchase #2	$158.88	5.842%	$168.1618	$168.16	$168.15	$168.20
Purchase #3	$44.51	6.818%	$47.5447	$47.54	$47.55	$47.50
Purchase #4	$124.32	13.785%	$141.4575	$141.46	$141.45	$141.50
Purchase #5	$237.90	13.814%	$270.7635	$270.76	$270.75	$270.80
Purchase #6	$209.68	5.684%	$221.5982	$221.60	$221.60	$221.60
Purchase #7	$216.83	9.578%	$237.598	$237.60	$237.60	$237.60
7 purchase totals =	$1,043.93		$1,141.6693	$1,141.67	$1,141.65	$1,141.70