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	$50.29	13.665%	$57.1621	$57.16	$57.15	$57.20
Purchase #2	$241.25	8.248%	$261.1483	$261.15	$261.15	$261.10
Purchase #3	$181.54	8.483%	$196.94	$196.94	$196.95	$196.90
Purchase #4	$38.94	12.525%	$43.8172	$43.82	$43.80	$43.80
Purchase #5	$67.88	3.162%	$70.0264	$70.03	$70.05	$70.00
Purchase #6	$178.71	3.276%	$184.5645	$184.56	$184.55	$184.60
Purchase #7	$141.26	10.622%	$156.2646	$156.26	$156.25	$156.30
7 purchase totals =	$899.87		$969.9231	$969.92	$969.90	$969.90