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	$160.67	13.658%	$182.6143	$182.61	$182.60	$182.60
Purchase #2	$127.90	8.215%	$138.407	$138.41	$138.40	$138.40
Purchase #3	$158.72	11.184%	$176.4712	$176.47	$176.45	$176.50
Purchase #4	$41.98	8.283%	$45.4572	$45.46	$45.45	$45.50
Purchase #5	$249.49	9.732%	$273.7704	$273.77	$273.75	$273.80
Purchase #6	$131.44	11.384%	$146.4031	$146.40	$146.40	$146.40
Purchase #7	$88.38	4.544%	$92.396	$92.40	$92.40	$92.40
7 purchase totals =	$958.58		$1,055.5192	$1,055.52	$1,055.45	$1,055.60