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	$38.93	3.871%	$40.437	$40.44	$40.45	$40.40
Purchase #2	$61.54	10.348%	$67.9082	$67.91	$67.90	$67.90
Purchase #3	$182.58	7.480%	$196.237	$196.24	$196.25	$196.20
Purchase #4	$132.44	6.515%	$141.0685	$141.07	$141.05	$141.10
Purchase #5	$19.35	7.540%	$20.809	$20.81	$20.80	$20.80
Purchase #6	$241.43	5.716%	$255.2301	$255.23	$255.25	$255.20
Purchase #7	$81.96	8.736%	$89.12	$89.12	$89.10	$89.10
7 purchase totals =	$758.23		$810.8098	$810.82	$810.80	$810.70