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	$213.64	11.616%	$238.4564	$238.46	$238.45	$238.50
Purchase #2	$114.38	7.797%	$123.2982	$123.30	$123.30	$123.30
Purchase #3	$82.70	9.198%	$90.3067	$90.31	$90.30	$90.30
Purchase #4	$10.99	5.439%	$11.5877	$11.59	$11.60	$11.60
Purchase #5	$32.79	3.569%	$33.9603	$33.96	$33.95	$34.00
Purchase #6	$78.93	6.322%	$83.92	$83.92	$83.90	$83.90
Purchase #7	$225.28	7.334%	$241.802	$241.80	$241.80	$241.80
7 purchase totals =	$758.71		$823.3313	$823.34	$823.30	$823.40