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	$38.36	12.720%	$43.2394	$43.24	$43.25	$43.20
Purchase #2	$84.67	6.550%	$90.2159	$90.22	$90.20	$90.20
Purchase #3	$85.43	4.755%	$89.4922	$89.49	$89.50	$89.50
Purchase #4	$55.40	4.347%	$57.8082	$57.81	$57.80	$57.80
Purchase #5	$232.50	3.645%	$240.9746	$240.97	$240.95	$241.00
Purchase #6	$222.54	10.396%	$245.6753	$245.68	$245.70	$245.70
Purchase #7	$98.51	4.860%	$103.2976	$103.30	$103.30	$103.30
7 purchase totals =	$817.41		$870.7032	$870.71	$870.70	$870.70