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	$19.70	3.455%	$20.3806	$20.38	$20.40	$20.40
Purchase #2	$54.82	4.838%	$57.4722	$57.47	$57.45	$57.50
Purchase #3	$187.37	9.349%	$204.8872	$204.89	$204.90	$204.90
Purchase #4	$81.43	7.242%	$87.3272	$87.33	$87.35	$87.30
Purchase #5	$128.46	9.468%	$140.6226	$140.62	$140.60	$140.60
Purchase #6	$97.32	10.113%	$107.162	$107.16	$107.15	$107.20
Purchase #7	$197.59	5.287%	$208.0366	$208.04	$208.05	$208.00
7 purchase totals =	$766.69		$825.8884	$825.89	$825.90	$825.90