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	$66.78	10.690%	$73.9188	$73.92	$73.90	$73.90
Purchase #2	$231.91	3.617%	$240.2982	$240.30	$240.30	$240.30
Purchase #3	$213.45	4.184%	$222.3807	$222.38	$222.40	$222.40
Purchase #4	$78.40	9.589%	$85.9178	$85.92	$85.90	$85.90
Purchase #5	$121.70	8.712%	$132.3025	$132.30	$132.30	$132.30
Purchase #6	$157.31	13.175%	$178.0356	$178.04	$178.05	$178.00
Purchase #7	$114.48	13.212%	$129.6051	$129.61	$129.60	$129.60
7 purchase totals =	$984.03		$1,062.4587	$1,062.47	$1,062.45	$1,062.40