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	$44.84	4.375%	$46.8018	$46.80	$46.80	$46.80
Purchase #2	$71.90	9.524%	$78.7478	$78.75	$78.75	$78.70
Purchase #3	$68.50	6.175%	$72.7299	$72.73	$72.75	$72.70
Purchase #4	$38.95	9.379%	$42.6031	$42.60	$42.60	$42.60
Purchase #5	$249.38	12.565%	$280.7146	$280.71	$280.70	$280.70
Purchase #6	$49.31	4.186%	$51.3741	$51.37	$51.35	$51.40
Purchase #7	$25.27	4.432%	$26.39	$26.39	$26.40	$26.40
7 purchase totals =	$548.15		$599.3613	$599.35	$599.35	$599.30