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	$85.72	5.826%	$90.714	$90.71	$90.70	$90.70
Purchase #2	$143.89	10.539%	$159.0546	$159.05	$159.05	$159.10
Purchase #3	$111.68	7.372%	$119.913	$119.91	$119.90	$119.90
Purchase #4	$153.56	13.572%	$174.4012	$174.40	$174.40	$174.40
Purchase #5	$164.92	3.297%	$170.3574	$170.36	$170.35	$170.40
Purchase #6	$129.44	8.721%	$140.7285	$140.73	$140.75	$140.70
Purchase #7	$73.29	7.159%	$78.5368	$78.54	$78.55	$78.50
7 purchase totals =	$862.50		$933.7055	$933.70	$933.70	$933.70