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	$243.56	12.167%	$273.1939	$273.19	$273.20	$273.20
Purchase #2	$138.74	4.508%	$144.9944	$144.99	$145.00	$145.00
Purchase #3	$29.50	11.282%	$32.8282	$32.83	$32.85	$32.80
Purchase #4	$201.40	12.512%	$226.5992	$226.60	$226.60	$226.60
Purchase #5	$192.32	4.287%	$200.5648	$200.56	$200.55	$200.60
Purchase #6	$56.47	5.534%	$59.595	$59.60	$59.60	$59.60
Purchase #7	$77.50	4.327%	$80.8534	$80.85	$80.85	$80.90
7 purchase totals =	$939.49		$1,018.6289	$1,018.62	$1,018.65	$1,018.70