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	$34.69	10.711%	$38.4056	$38.41	$38.40	$38.40
Purchase #2	$50.95	3.555%	$52.7613	$52.76	$52.75	$52.80
Purchase #3	$164.43	11.385%	$183.1504	$183.15	$183.15	$183.20
Purchase #4	$217.31	13.223%	$246.0449	$246.04	$246.05	$246.00
Purchase #5	$145.80	13.816%	$165.9437	$165.94	$165.95	$165.90
Purchase #6	$78.48	13.430%	$89.0199	$89.02	$89.00	$89.00
Purchase #7	$246.59	6.845%	$263.4691	$263.47	$263.45	$263.50
7 purchase totals =	$938.25		$1,038.7949	$1,038.79	$1,038.75	$1,038.80