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	$237.32	9.261%	$259.2982	$259.30	$259.30	$259.30
Purchase #2	$124.76	11.794%	$139.4742	$139.47	$139.45	$139.50
Purchase #3	$145.31	10.339%	$160.3336	$160.33	$160.35	$160.30
Purchase #4	$231.46	13.330%	$262.3136	$262.31	$262.30	$262.30
Purchase #5	$53.46	3.778%	$55.4797	$55.48	$55.50	$55.50
Purchase #6	$111.75	5.238%	$117.6035	$117.60	$117.60	$117.60
Purchase #7	$87.71	4.765%	$91.8894	$91.89	$91.90	$91.90
7 purchase totals =	$991.77		$1,086.3922	$1,086.38	$1,086.40	$1,086.40