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	$242.43	12.813%	$273.4926	$273.49	$273.50	$273.50
Purchase #2	$104.43	10.208%	$115.0902	$115.09	$115.10	$115.10
Purchase #3	$169.94	3.818%	$176.4283	$176.43	$176.45	$176.40
Purchase #4	$97.57	6.137%	$103.5579	$103.56	$103.55	$103.60
Purchase #5	$40.38	11.641%	$45.0806	$45.08	$45.10	$45.10
Purchase #6	$127.51	13.591%	$144.8399	$144.84	$144.85	$144.80
Purchase #7	$245.50	11.221%	$273.0476	$273.05	$273.05	$273.00
7 purchase totals =	$1,027.76		$1,131.5371	$1,131.54	$1,131.60	$1,131.50