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	$242.86	5.224%	$255.547	$255.55	$255.55	$255.50
Purchase #2	$245.32	9.117%	$267.6858	$267.69	$267.70	$267.70
Purchase #3	$223.40	8.352%	$242.0584	$242.06	$242.05	$242.10
Purchase #4	$48.70	12.397%	$54.7373	$54.74	$54.75	$54.70
Purchase #5	$240.47	12.840%	$271.3463	$271.35	$271.35	$271.30
Purchase #6	$104.65	4.570%	$109.4325	$109.43	$109.45	$109.40
Purchase #7	$81.46	8.666%	$88.5193	$88.52	$88.50	$88.50
7 purchase totals =	$1,186.86		$1,289.3266	$1,289.34	$1,289.35	$1,289.20