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	$208.51	9.541%	$228.4039	$228.40	$228.40	$228.40
Purchase #2	$35.50	13.476%	$40.284	$40.28	$40.30	$40.30
Purchase #3	$159.77	9.102%	$174.3123	$174.31	$174.30	$174.30
Purchase #4	$216.39	12.709%	$243.891	$243.89	$243.90	$243.90
Purchase #5	$226.29	5.597%	$238.9555	$238.96	$238.95	$239.00
Purchase #6	$74.99	12.396%	$84.2858	$84.29	$84.30	$84.30
Purchase #7	$78.31	13.663%	$89.0095	$89.01	$89.00	$89.00
7 purchase totals =	$999.76		$1,099.1420	$1,099.14	$1,099.15	$1,099.20