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	$73.37	13.650%	$83.385	$83.39	$83.40	$83.40
Purchase #2	$78.60	5.654%	$83.044	$83.04	$83.05	$83.00
Purchase #3	$218.54	10.578%	$241.6572	$241.66	$241.65	$241.70
Purchase #4	$72.81	13.268%	$82.4704	$82.47	$82.45	$82.50
Purchase #5	$82.86	9.474%	$90.7102	$90.71	$90.70	$90.70
Purchase #6	$103.46	4.355%	$107.9657	$107.97	$107.95	$108.00
Purchase #7	$112.53	7.734%	$121.2331	$121.23	$121.25	$121.20
7 purchase totals =	$742.17		$810.4656	$810.47	$810.45	$810.50