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	$241.50	11.778%	$269.9439	$269.94	$269.95	$269.90
Purchase #2	$231.60	6.149%	$245.8411	$245.84	$245.85	$245.80
Purchase #3	$142.79	11.431%	$159.1123	$159.11	$159.10	$159.10
Purchase #4	$111.27	3.758%	$115.4515	$115.45	$115.45	$115.50
Purchase #5	$123.83	6.333%	$131.6722	$131.67	$131.65	$131.70
Purchase #6	$182.56	4.354%	$190.5087	$190.51	$190.50	$190.50
Purchase #7	$196.90	8.563%	$213.7605	$213.76	$213.75	$213.80
7 purchase totals =	$1,230.45		$1,326.2902	$1,326.28	$1,326.25	$1,326.30