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	$159.30	3.626%	$165.0762	$165.08	$165.10	$165.10
Purchase #2	$27.54	3.548%	$28.5171	$28.52	$28.50	$28.50
Purchase #3	$136.64	11.455%	$152.2921	$152.29	$152.30	$152.30
Purchase #4	$38.80	12.842%	$43.7827	$43.78	$43.80	$43.80
Purchase #5	$92.50	9.775%	$101.5419	$101.54	$101.55	$101.50
Purchase #6	$164.37	7.291%	$176.3542	$176.35	$176.35	$176.40
Purchase #7	$86.48	3.145%	$89.1998	$89.20	$89.20	$89.20
7 purchase totals =	$705.63		$756.7640	$756.76	$756.80	$756.80