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	$108.37	11.813%	$121.1717	$121.17	$121.15	$121.20
Purchase #2	$16.57	12.206%	$18.5925	$18.59	$18.60	$18.60
Purchase #3	$186.28	7.504%	$200.2585	$200.26	$200.25	$200.30
Purchase #4	$196.61	9.526%	$215.3391	$215.34	$215.35	$215.30
Purchase #5	$180.89	13.235%	$204.8308	$204.83	$204.85	$204.80
Purchase #6	$36.94	10.523%	$40.8272	$40.83	$40.85	$40.80
Purchase #7	$181.38	9.617%	$198.8233	$198.82	$198.80	$198.80
7 purchase totals =	$907.04		$999.8431	$999.84	$999.85	$999.80