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	$127.57	9.184%	$139.286	$139.29	$139.30	$139.30
Purchase #2	$104.39	10.473%	$115.3228	$115.32	$115.30	$115.30
Purchase #3	$158.69	11.572%	$177.0536	$177.05	$177.05	$177.10
Purchase #4	$18.41	11.492%	$20.5257	$20.53	$20.55	$20.50
Purchase #5	$82.57	4.848%	$86.573	$86.57	$86.55	$86.60
Purchase #6	$57.54	7.332%	$61.7588	$61.76	$61.75	$61.80
Purchase #7	$90.45	7.667%	$97.3848	$97.38	$97.40	$97.40
7 purchase totals =	$639.62		$697.9047	$697.90	$697.90	$698.00