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	$155.59	5.523%	$164.1832	$164.18	$164.20	$164.20
Purchase #2	$185.81	9.727%	$203.8837	$203.88	$203.90	$203.90
Purchase #3	$210.40	9.159%	$229.6705	$229.67	$229.65	$229.70
Purchase #4	$8.89	13.602%	$10.0992	$10.10	$10.10	$10.10
Purchase #5	$35.84	12.635%	$40.3684	$40.37	$40.35	$40.40
Purchase #6	$154.39	3.118%	$159.2039	$159.20	$159.20	$159.20
Purchase #7	$106.88	4.239%	$111.4106	$111.41	$111.40	$111.40
7 purchase totals =	$857.80		$918.8195	$918.81	$918.80	$918.90