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	$247.64	4.572%	$258.9621	$258.96	$258.95	$259.00
Purchase #2	$52.38	12.829%	$59.0998	$59.10	$59.10	$59.10
Purchase #3	$185.82	7.859%	$200.4236	$200.42	$200.40	$200.40
Purchase #4	$25.39	12.126%	$28.4688	$28.47	$28.45	$28.50
Purchase #5	$213.96	11.758%	$239.1174	$239.12	$239.10	$239.10
Purchase #6	$81.50	10.537%	$90.0877	$90.09	$90.10	$90.10
Purchase #7	$64.80	12.296%	$72.7678	$72.77	$72.75	$72.80
7 purchase totals =	$871.49		$948.9272	$948.93	$948.85	$949.00