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	$144.82	9.115%	$158.0203	$158.02	$158.00	$158.00
Purchase #2	$241.89	3.452%	$250.24	$250.24	$250.25	$250.20
Purchase #3	$50.89	12.855%	$57.4319	$57.43	$57.45	$57.40
Purchase #4	$240.78	11.240%	$267.8437	$267.84	$267.85	$267.80
Purchase #5	$176.74	11.407%	$196.9007	$196.90	$196.90	$196.90
Purchase #6	$8.59	11.522%	$9.5797	$9.58	$9.60	$9.60
Purchase #7	$140.28	12.188%	$157.3773	$157.38	$157.40	$157.40
7 purchase totals =	$1,003.99		$1,097.3936	$1,097.39	$1,097.45	$1,097.30