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	$80.68	5.605%	$85.2021	$85.20	$85.20	$85.20
Purchase #2	$5.92	7.767%	$6.3798	$6.38	$6.40	$6.40
Purchase #3	$18.56	9.504%	$20.3239	$20.32	$20.30	$20.30
Purchase #4	$137.29	12.572%	$154.5501	$154.55	$154.55	$154.60
Purchase #5	$126.88	9.143%	$138.4806	$138.48	$138.50	$138.50
Purchase #6	$102.33	13.829%	$116.4812	$116.48	$116.50	$116.50
Purchase #7	$159.35	3.111%	$164.3074	$164.31	$164.30	$164.30
7 purchase totals =	$631.01		$685.7251	$685.72	$685.75	$685.80