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	$217.79	9.589%	$238.6739	$238.67	$238.65	$238.70
Purchase #2	$241.84	4.725%	$253.2669	$253.27	$253.25	$253.30
Purchase #3	$204.53	3.391%	$211.4656	$211.47	$211.45	$211.50
Purchase #4	$185.95	7.401%	$199.7122	$199.71	$199.70	$199.70
Purchase #5	$44.60	12.845%	$50.3289	$50.33	$50.35	$50.30
Purchase #6	$247.29	7.179%	$265.0429	$265.04	$265.05	$265.00
Purchase #7	$54.83	11.812%	$61.3065	$61.31	$61.30	$61.30
7 purchase totals =	$1,196.83		$1,279.7969	$1,279.80	$1,279.75	$1,279.80