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	$238.29	3.418%	$246.4348	$246.43	$246.45	$246.40
Purchase #2	$142.39	11.778%	$159.1607	$159.16	$159.15	$159.20
Purchase #3	$172.31	7.582%	$185.3745	$185.37	$185.35	$185.40
Purchase #4	$214.68	13.156%	$242.9233	$242.92	$242.90	$242.90
Purchase #5	$110.41	5.549%	$116.5367	$116.54	$116.55	$116.50
Purchase #6	$78.83	7.463%	$84.7131	$84.71	$84.70	$84.70
Purchase #7	$100.71	3.423%	$104.1573	$104.16	$104.15	$104.20
7 purchase totals =	$1,057.62		$1,139.3004	$1,139.29	$1,139.25	$1,139.30