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	$135.83	3.518%	$140.6085	$140.61	$140.60	$140.60
Purchase #2	$10.77	9.459%	$11.7887	$11.79	$11.80	$11.80
Purchase #3	$51.80	6.379%	$55.1043	$55.10	$55.10	$55.10
Purchase #4	$221.50	13.146%	$250.6184	$250.62	$250.60	$250.60
Purchase #5	$168.30	7.604%	$181.0975	$181.10	$181.10	$181.10
Purchase #6	$85.72	5.831%	$90.7183	$90.72	$90.70	$90.70
Purchase #7	$249.93	4.216%	$260.467	$260.47	$260.45	$260.50
7 purchase totals =	$923.85		$990.4027	$990.41	$990.35	$990.40